Heart

IWBCA
Feb 15
11 min read

The heart is a muscular organ that keeps blood moving through the lungs and the rest of the body, using coordinated muscle contractions, valves, and electrical signals to deliver oxygen and nutrients and remove waste products every moment of life.

Overview

What is the heart and what does it do?

The heart is a hollow, muscular organ in the center of the chest that works as the body’s main pump. With every beat, it pushes blood to the lungs to pick up oxygen, and then out to the rest of the body to supply organs and tissues. It works continuously, adjusting its rate and force to match the body's needs at rest, during sleep, and during activity.

Continuous Circulation: The heart keeps blood moving in a closed loop. One side sends blood to the lungs, and the other side sends blood to the body. This circulation provides oxygen, carries away carbon dioxide and other waste products, and delivers hormones, immune cells, and nutrients wherever they are needed.
Dual Pump Design: The heart has two main sides that work together but perform different tasks. The right side receives blood that has already delivered oxygen to the body and sends it to the lungs. The left side receives freshly oxygenated blood from the lungs and sends it to the brain, kidneys, muscles, and all other organs.
Automatic Function: The heart generates its own electrical impulses and can keep beating without conscious control. Specialized cells in the conduction system coordinate each beat so that the chambers squeeze in the right sequence and blood flows efficiently.
Adaptation to Demand: The heart adjusts its output from minute to minute. When a person stands up, exercises, becomes ill, or feels strong emotions, the heart rate and the strength of contraction change so that blood pressure and organ perfusion remain adequate.

Anatomy

What are the main structures and chambers of the heart?

The heart sits behind the breastbone, slightly left of center, and is enclosed in a protective sac called the pericardium. Its internal structure is divided into four chambers with valves that direct blood flow in only one direction.

Chambers: The heart has two upper chambers called atria and two lower chambers called ventricles. The right atrium and right ventricle handle blood returning from the body and send it to the lungs. The left atrium and left ventricle handle blood returning from the lungs and send it out to the body. The left ventricle has the thickest wall because it must generate enough force to pump blood through the entire body.
Valves: Four valves act as one-way doors inside the heart. The tricuspid valve separates the right atrium from the right ventricle. The pulmonary valve sits between the right ventricle and the pulmonary artery. The mitral valve separates the left atrium from the left ventricle. The aortic valve sits between the left ventricle and the aorta. These valves open and close with each heartbeat to keep blood flowing forward and prevent backward leakage.
Heart Wall Layers: The wall of the heart has three main layers. The inner lining, called the endocardium, provides a smooth surface for blood flow. The middle muscular layer, the myocardium, generates the force that pumps blood. The outer layer, the epicardium, lies directly against the pericardial space and helps protect the heart.
Pericardium: The pericardium is a double-layered sac that surrounds the heart. A small amount of fluid between its layers allows the heart to move and beat without friction against surrounding structures. The pericardium helps limit excessive motion and sudden stretching of the heart.
Great Vessels: Large arteries and veins connect the heart to the rest of the circulation. The venae cavae bring blood from the body into the right atrium. The pulmonary arteries carry blood from the right ventricle to the lungs. The pulmonary veins return oxygenated blood from the lungs to the left atrium. The aorta carries blood from the left ventricle to the entire body.

Blood Flow and Circulation

How does blood travel through the heart and the rest of the body?

Blood follows a precise pathway through the heart, lungs, and body. Each heartbeat moves blood in a coordinated sequence so that low-oxygen blood is refreshed in the lungs and high-oxygen blood reaches the organs.

Right-Sided Circulation to the Lungs: Blood that has delivered oxygen to the body returns through the venae cavae to the right atrium. When the right atrium contracts, blood passes through the tricuspid valve into the right ventricle. When the right ventricle contracts, it pushes blood through the pulmonary valve into the pulmonary arteries and on to the lungs, where carbon dioxide is released, and oxygen is taken up.
Left-Sided Circulation to the Body: Oxygen-rich blood flows from the lungs through the pulmonary veins into the left atrium. When the left atrium contracts, blood passes through the mitral valve into the left ventricle. When the left ventricle contracts, it ejects blood through the aortic valve into the aorta, which branches into arteries that supply the brain, heart muscle, kidneys, digestive organs, muscles, and all other tissues.
Cardiac Cycle Phases: Each heartbeat follows a cycle of filling and ejection. During diastole, the ventricles relax and fill with blood from the atria. During systole, the ventricles contract to eject blood into the arteries. The valves open and close in a set order so that blood does not flow backward during these transitions.
Systemic and Pulmonary Circulation: The heart supports two linked circulatory loops. The pulmonary circulation moves blood between the heart and lungs, while the systemic circulation moves blood between the heart and the rest of the body. The right ventricle powers the pulmonary loop, and the left ventricle powers the systemic loop.

Electrical System

How does the heart coordinate each beat?

The heart’s pumping action depends on an internal electrical system that triggers and synchronizes muscle contraction. This system ensures that the atria contract first, followed by the ventricles, so that each stroke of the heart is efficient.

Pacemaker Cells: Specialized cells in the sinoatrial node in the right atrium generate regular electrical impulses. This structure serves as the heart’s natural pacemaker. Its rate is influenced by signals from the autonomic nervous system, circulating hormones, and internal feedback from blood pressure and oxygen levels.
Conduction Pathways: From the sinoatrial node, the impulse spreads through the atrial muscle and reaches the atrioventricular node. After a brief pause that allows the ventricles to finish filling, the impulse travels down the bundle of His, through the right and left bundle branches, and into a network of Purkinje fibers that distribute the signal rapidly through the ventricular muscle.
Coordination of Contraction: This conduction pattern causes the atria to contract first, pushing blood into the ventricles, followed by nearly simultaneous contraction of both ventricles, ejecting blood to the lungs and body. Disruptions of this pattern can cause arrhythmias, which may range from harmless to life-threatening.
Electrical Signatures on Electrocardiogram: The electrical activity of the heart can be recorded on the skin as an electrocardiogram. The P wave reflects atrial activation, the QRS complex reflects ventricular activation, and the T wave reflects ventricular recovery. Changes in these patterns can reveal problems with rhythm, conduction, or the heart muscle.

Blood Supply and Metabolic Demands

How does the heart receive its own blood supply and meet its energy needs?

The heart muscle works constantly and has a high demand for oxygen and nutrients. It relies on its own set of arteries and veins to meet these needs.

Coronary Arteries: The coronary arteries branch off from the base of the aorta just above the aortic valve. The right and left coronary arteries and their branches wrap around the surface of the heart and dive into the muscle. They supply oxygen-rich blood to the myocardium, allowing it to continue contracting effectively.
Coronary Veins: After passing through the heart muscle, blood returns through the coronary veins into the coronary sinus and then into the right atrium. This separate return path allows the heart to clear waste products and maintain normal function.
High Oxygen Demand: Because the heart rarely rests, its oxygen extraction from blood is already high at baseline. During exertion, increased coronary blood flow is needed to meet the higher metabolic demands. Narrowing of the coronary arteries limits this ability and can lead to chest discomfort or more severe damage.
Vulnerability to Ischemia: If a coronary artery is suddenly blocked, the region of heart muscle supplied by that artery can be deprived of oxygen. Prolonged interruption of flow can cause permanent damage to the myocardium. This makes the coronary circulation a central focus in cardiovascular health and disease.

Heart and Other Organ Systems

How does the heart interact with other organs and body systems?

The heart does not act alone. It works closely with other organs and regulatory systems to maintain stable blood pressure, adequate oxygen delivery, and balanced fluid and salt levels.

Coordination with the Lungs: The heart and lungs work together as a single functional unit for gas exchange. The right ventricle must match the capacity of the pulmonary circulation, and changes in lung pressure or disease can strain this side of the heart.
Interaction with the Kidneys: The kidneys sense blood flow and blood pressure and adjust salt and water excretion to support circulation. Hormones produced by the kidneys and related pathways influence heart workload, vascular tone, and long-term blood pressure.
Influence of the Nervous System: The autonomic nervous system can increase or decrease heart rate and contractility. The sympathetic branch accelerates the heart and strengthens contraction during stress or activity, while the parasympathetic branch slows the heart during rest.
Endocrine Signals: Hormones such as adrenaline, thyroid hormone, and others modify heart rate, contractility, and vascular tone. The heart itself releases hormones such as natriuretic peptides that help regulate blood volume and pressure.

Common Heart Conditions

What are some common disorders that affect the heart?

Many conditions can alter how the heart works. Some primarily affect the coronary arteries, some involve the valves or muscle, and others involve the electrical system.

Coronary Artery Disease: Narrowing or blockage of the coronary arteries by atherosclerotic plaque can reduce blood flow to the heart muscle. This can cause chest discomfort, shortness of breath, or a heart attack when blood flow becomes critically limited or is suddenly interrupted.
Heart Failure: Heart failure occurs when the heart cannot pump enough blood to meet the body’s needs or can only do so at elevated filling pressures. This can result from weakened muscle, stiff chambers, valve disease, or long-standing high blood pressure and often leads to fatigue, shortness of breath, and fluid retention.
Cardiomyopathies: Cardiomyopathies are diseases of the heart muscle. The heart may become enlarged and weak, thickened and stiff, or structurally abnormal due to genetic, metabolic, inflammatory, or toxic causes. These changes can impair pumping and predispose to arrhythmias.
Valve Disease: Valve problems include stenosis, where a valve does not open fully, and regurgitation, where a valve does not close fully, allowing blood to leak backward. Valve disease can increase the workload on the chambers, lead to enlargement, and eventually cause symptoms if left untreated.
Arrhythmias: Arrhythmias are disturbances of heart rhythm. They include rhythms that are too fast, too slow, or irregular. Some cause palpitations or brief dizziness, while others can lead to fainting or sudden cardiac arrest.
Congenital Heart Disease: Congenital heart disease refers to structural problems present at birth, such as holes between chambers, abnormal connections, or malformed valves. Severity ranges from minor defects that need only monitoring to complex malformations that require surgery.

Diagnosis and Testing

How do clinicians evaluate the heart and its function?

Assessment of the heart relies on a combination of history, physical examination, and tests that visualize structure and measure function. The choice of tests depends on the questions that need to be answered.

Clinical Assessment: A clinician begins by asking about symptoms such as chest pain, shortness of breath, palpitations, fainting, swelling, and exercise tolerance. The physical examination may reveal abnormal heart sounds, murmurs from turbulent flow, extra fluid in the lungs, or swelling in the legs that suggests circulatory problems.
Electrocardiogram: An electrocardiogram records the electrical activity of the heart through electrodes placed on the skin. It can identify arrhythmias, conduction delays, evidence of prior heart attacks, and some forms of chamber enlargement.
Echocardiography: Echocardiography uses ultrasound to create real-time images of the heart. It shows chamber size, wall thickness, valve structure and function, pumping strength, and patterns of blood flow. It is central to evaluating suspected heart failure, valve disease, congenital defects, and many other conditions.
Stress Testing: Stress tests assess the heart’s response to increased workload. Exercise or medications are used to increase heart rate and cardiac workload, while electrocardiogram and imaging data are collected. Stress testing helps identify coronary artery disease and evaluate functional capacity.
Cardiac Imaging: Additional imaging techniques, such as cardiac magnetic resonance imaging and computed tomography, can provide detailed information about the heart's structure, tissue characteristics, coronary arteries, and surrounding vessels. These tests refine diagnosis and guide planning for procedures.
Cardiac Catheterization: Cardiac catheterization involves inserting thin tubes into arteries or veins and advancing them to the heart. It allows direct measurement of pressures and oxygen levels and visualization of coronary arteries with contrast. It is often used when an intervention, such as stenting or valve procedures, is being considered.

Protection and Prevention

How can people support a healthy heart and reduce the risk of disease?

While some heart conditions are inherited or present at birth, many common heart problems are influenced by everyday choices and long-term risk factors. Addressing those factors early can reduce the likelihood of disease and improve outcomes when disease is present.

Avoiding Tobacco: Avoiding cigarettes and other tobacco products is one of the most important steps in protecting the heart and blood vessels. Tobacco exposure accelerates atherosclerosis, raises blood pressure, and increases the risk of heart attacks and strokes.
Supporting Healthy Blood Pressure and Cholesterol: Keeping blood pressure and cholesterol within recommended ranges through food choices, physical activity, and medications when needed reduces stress on the heart and slows plaque buildup in the coronary arteries.
Managing Blood Sugar: Good blood sugar control in diabetes reduces damage to blood vessels and nerves that support heart function. Early attention to insulin resistance and metabolic health helps lower long-term cardiac risk.
Staying Active: Regular physical activity improves exercise capacity, blood pressure, lipid profiles, and weight management. Even modest increases in daily physical activity have measurable benefits for heart health, especially when sustained over time.
Food Patterns That Support Cardiovascular Health: Eating patterns that emphasize vegetables, fruits, whole grains, legumes, lean proteins, and unsaturated fats and that limit highly processed foods, added sugars, and very high saturated fat intake support the heart and vascular system.
Monitoring and Regular Checkups: Routine checkups enable early detection of high blood pressure, high cholesterol, arrhythmias, and the early signs of heart disease. Screening and follow-up plans are tailored to age, family history, and other risk factors, guiding decisions about lifestyle changes and medications.

Living With Heart Disease

What should people know if they have a heart condition or are at increased risk?

For many heart conditions, advances in diagnosis and treatment have transformed outcomes. People often live for many years with stable heart disease when risk factors are controlled, and treatment plans are followed.

Understanding the Specific Diagnosis: Each heart condition has its own causes, usual course, and treatment options. Clear information about the specific diagnosis, the goals of therapy, and warning signs to watch for helps people participate in decisions and respond promptly to changes.
Medication Adherence: Many heart conditions require long-term medications to manage blood pressure, rhythm, fluid balance, or clotting risk. Taking medicines exactly as prescribed and discussing any concerns or side effects with clinicians is central to effective management.
Symptom Monitoring: Changes in exercise tolerance, new or worsening shortness of breath, chest discomfort, palpitations, swelling, or episodes of fainting should be reported promptly. Early attention to these signals can prevent more serious events.
Collaboration with the Care Team: Ongoing partnership with primary care clinicians, cardiologists, nurses, rehabilitation specialists, and other professionals supports both day-to-day health and long-term outcomes. Cardiac rehabilitation and education programs can provide structured support for activity, food choices, and coping with a chronic condition.

By understanding how the heart is built, how it works, and what can go wrong, people and clinicians can work together to protect its function and respond effectively when problems arise.

The IWBCA provides the information and materials on this site for educational and informational purposes only. The content is not a substitute for professional medical evaluation, diagnosis, or treatment. Always consult your physician or another qualified healthcare provider regarding any questions you may have about a medical condition, diagnosis, or course of treatment. Do not disregard, delay, or alter medical advice based on information obtained from this site. If you believe you are experiencing a medical emergency, call 911 or your local emergency services immediately.