Heart

The heart is a muscular organ found in humans and other animals. It pumps blood through the blood vessels, delivering oxygen and nutrients to the body’s tissues while removing waste products like carbon dioxide. In humans, the heart is about the size of a closed fist and sits between the lungs in the chest area known as the mediastinum.

The heart has four chambers: two upper chambers called atria and two lower chambers called ventricles. Blood flows through the heart in one direction thanks to special structures called heart valves. The heart’s rhythm is controlled by pacemaker cells that send electrical signals, causing the heart to beat regularly. A healthy adult heart beats about 72 times per minute at rest.

Cardiovascular diseases are the leading cause of death worldwide. Common problems include coronary artery disease and stroke. Factors that increase risk include smoking, being overweight, and having high blood pressure or diabetes. Doctors called cardiologists specialize in diagnosing and treating heart conditions using tools like ECG and echocardiogram.

Structure

The heart is a muscular organ that pumps blood through the body. It is located in the chest, surrounded by a sac called the pericardium. The heart has four chambers: two upper atria that receive blood, and two lower ventricles that pump blood out.

The heart has four valves that keep blood flowing in the right direction. These valves are located between the atria and ventricles, and at the exits of the ventricles. The walls of the heart are made of three layers: the inner endocardium, the middle myocardium, and the outer epicardium. The heart needs its own blood supply, which comes from the coronary arteries. Nerves also help control the heart’s rate and force of contraction.

Development

Development of the human heart during the first eight weeks (top) and the formation of the heart chambers (bottom). In this figure, the blue and red colors represent blood inflow and outflow (not venous and arterial blood). Initially, all venous blood flows from the tail/atria to the ventricles/head, a very different pattern from that of an adult.

The heart is the first organ to start working in a growing baby. It begins to beat and pump blood just about three weeks after a baby starts to form. This early beating is very important for the baby's growth before it is born.

The heart comes from special cells that form a tube. This tube folds and changes shape to make the heart we know. By about five weeks, walls form inside the heart to separate its parts. After the baby is born, a small opening in the heart closes up so blood flows the right way. The baby’s heart starts beating slowly and then speeds up before slowing down again as the baby grows.

Physiology

Main article: Cardiac physiology

Blood flow through the valves

The heart works like a pump to move blood through the body. It sends blood to the lungs to pick up oxygen and then pumps that oxygen-rich blood to the rest of the body. The right side of the heart collects blood that has less oxygen and sends it to the lungs, while the left side receives oxygen-rich blood from the lungs and sends it out to the body.

The heart beats in a regular pattern, contracting and relaxing to push blood out and then fill up again. This pattern, called the cardiac cycle, keeps blood moving smoothly through the body. The heart’s rhythm is controlled by special cells that send electrical signals to make the heart muscle contract.

Clinical significance

The stethoscope is a key tool in medicine, helping doctors listen to the heart and detect various conditions like heart murmurs.

Cardiovascular diseases are the leading cause of death worldwide, often related to lifestyle and aging. Heart disease is a major cause of death, especially in high-income countries.

Heart disease can take many forms, such as coronary artery disease, where fatty deposits narrow the arteries and may lead to chest pain or heart attacks. Heart failure occurs when the heart cannot pump enough blood, leading to symptoms like breathlessness and swelling. Other conditions include cardiomyopathies, which affect the heart muscle, and valvular heart disease, which involves problems with the heart valves. Arrhythmias, or irregular heart rhythms, can also occur and may need treatment.

History

Humans have known about the heart for a very long time, but its exact role and structure were hard to understand. In ancient times, people had many ideas about what the heart did. For example, Aristotle thought the heart made blood, while Plato believed it moved blood around the body.

Later, scientists learned more. In 1628, William Harvey explained how blood flows through the heart and body. This was a big step in understanding how our bodies work. Over time, doctors have made amazing advances, including performing the first human heart transplant in 1967 by Christiaan Barnard. Today, heart disease is one of the most common reasons people get very sick around the world.

Society and culture

The heart has great meaning in many cultures and religions. People have long thought of the heart as the center of feelings, thoughts, and life itself. In many beliefs, the heart is very important. For example, in some religions, the heart is seen as a place of truth, courage, or connection to a higher power.

In everyday life, the heart is also used in many expressions. For instance, people talk about having a "broken heart" when they feel sad after losing a loved one or a romantic partner. The heart shape is also a common symbol, especially around Valentine’s Day, representing love and affection. In food, animal hearts are eaten in many parts of the world. They are a type of offal, or organ meat, and are often used in many dishes, such as skewers or stews.

Other animals

The size of a heart changes a lot among different animals. In vertebrates, like mammals and birds, hearts range from very small in mice to extremely large in blue whales. These hearts are usually found in the middle of the body's underside, enclosed by a layer called the pericardium.

Most vertebrates have their hearts positioned on the left side of the body. This unusual placement might be due to how the embryo develops early in life. The heartbeat rate also varies widely; for example, codfish have hearts that beat about 20 times a minute, while some hummingbirds' hearts can beat up to 1,200 times a minute.