The heart is a muscle about the size of an adult fist. It is essentially a pump, and it beats up to 100,000 times a day. The heart has four valves and four chambers, which are connected to blood vessels. Veins are the blood vessels that carry blood from the body to the heart. Arteries are the vessels that carry blood away from the heart to the body.
There are two sides to the heart, separated by an inner wall, called the septum. The right side of the heart pumps blood to the lungs to pick up oxygen. The left side of the heart pumps the oxygen-rich blood to the body.
Four valves control the flow of blood from the atria to the ventricles and from the ventricles into the two large arteries connected to the heart.
The tricuspid valve is located in the right side of the heart, between the right atrium and the right ventricle. The pulmonary valve is located in the right side of the heart, between the right ventricle and the entrance to the pulmonary artery that carries blood to the lungs. The mitral valve is in the left side of the heart, between the left atrium and the left ventricle. The aortic valve is in the left side of the heart, between the left ventricle and the entrance to the aorta, the artery that carries blood to the body. These valves allow blood to flow through to the next chamber or to one of the arteries, and then they shut to keep blood from flowing back in. The opening and closing of the valves is what makes the “heartbeat” sound. The first part of the heart beat sound is made by the mitral and tricuspid valves closing at the beginning of systole (systole is when the ventricles contract, pumping blood out of the heart). The second part of the heartbeat sound is made by the aortic and pulmonary valves closing at beginning of diastole (diastole is when the ventricles relax and fill with blood pumped into them by the atria).
The heart has two chambers on the right side and two chambers on the left. The atria (two upper chambers) collect blood as it comes into the heart. The ventricles (two lower chambers) pump blood out of the heart to the lungs or other parts of the body.
The pulmonary veins carry oxygen-rich blood from the lungs to the left side of the heart, so it can be pumped out to the body. The vena cava are two large veins that carry oxygen-poor blood from the body back to the heart.
The aorta is the main artery that carries oxygen-rich blood pumped from the left side of the heart out to the body. The pulmonary artery carries blood pumped from the right side of the heart to the lungs to pick up a fresh supply of oxygen. The coronary arteries carry oxygen-rich blood from the aorta to the heart muscle, which must have its own blood supply to function.