Heart

The heart is a muscular organ found in humans and other animals. It pumps blood through the blood vessels, giving oxygen and nutrients to the body’s tissues. It also helps remove waste like carbon dioxide. In humans, the heart is about the size of a closed fist and sits between the lungs in the chest area called the mediastinum.

The heart has four chambers: two upper chambers called atria and two lower chambers called ventricles. Blood moves through the heart in one direction because of special structures called heart valves. The heart’s rhythm is controlled by pacemaker cells that send electrical signals, making the heart beat regularly. A healthy adult heart beats about 72 times per minute when resting.

Cardiovascular diseases can affect the heart. Common problems include coronary artery disease and stroke. Things that can increase risk include smoking, being overweight, and having high blood pressure or diabetes. Doctors called cardiologists help diagnose and treat heart conditions using tools like ECG and echocardiogram.

Structure

The heart is a muscular organ that pumps blood through the body. It is 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 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 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 work in a growing baby. It starts beating and pumping blood about three weeks after the baby begins to form. This early beating is very important for the baby's growth before it is born.

The heart forms from special cells that create a tube. This tube folds and changes shape to become the heart. 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 so blood can flow properly. The baby’s heart starts beating slowly, then speeds up, and later slows down 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 get oxygen and then pumps this oxygen-rich blood to the rest of the body. The right side of the heart collects blood with less oxygen and sends it to the lungs. The left side gets oxygen-rich blood from the lungs and sends it to the body.

The heart beats in a regular pattern, squeezing to push blood out and then relaxing to fill up again. This pattern, called the cardiac cycle, keeps blood moving smoothly. Special cells control the heart’s rhythm by sending signals to make the heart muscle squeeze.

Clinical significance

The stethoscope is a key tool in medicine. It helps doctors listen to the heart and find problems such as heart murmurs.

Heart disease can affect the heart in many ways. Some types include problems with the arteries, the heart muscle, or the heart valves. These conditions can sometimes cause symptoms like pain or breathlessness.

History

Humans have known about the heart for a very long time, but it was hard to understand what it does. In the past, people had many ideas about the heart. 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 learning how our bodies work. Over time, doctors have made great advances, including 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 means a lot 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 or courage.

In everyday life, the heart is 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 very 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 on the left side of the body. This might be because of how the embryo develops early in life. The heartbeat rate also varies a lot; 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.