There are four valves within the heart:
- The tricuspid valve is between the right atrium and the right ventricle.
- The pulmonary valve is between the right ventricle and the pulmonary artery.
- The mitral valve is between the left atrium and the left ventricle.
- The aortic valve is located between the left ventricle and the aorta.
These valves open when blood passes through them and then close to keep the blood from flowing in the wrong direction.
The four chambers of the heart are attached to major veins or arteries that either bring blood into or carry blood away from the heart.
The atria are the receiving stations of the heart. The right atrium receives its supply of oxygen-poor blood from the two largest veins in the body, the superior and inferior vena cava.
The left atrium receives blood that has been oxygenated in the lungs from the pulmonary veins. Both atria then pump their supply of blood into the ventricles.
The ventricles are the shipping stations of the heart. The right ventricle pumps oxygen-poor blood into the lungs through the pulmonary artery while the left ventricle pumps oxygenated blood to the body through the aorta, the largest artery in the body.
The heart wall consists of three layers: the endocardium, myocardium and epicardium.
The endocardium is the thin membrane that lines the interior of the heart.
The myocardium is the middle layer of the heart. It is the heart muscle and is the thickest layer of the heart.
The epicardium is a thin layer on the surface of the heart in which the coronary arteries lie.
The pericardium is a thin sac the heart sits in, often filled with a small amount of fluid, which separates the heart from the other structures in the chest such as the lungs.
The conduction system is the heart's own built-in pacemaker. This special tissue sets the heart rate and allows the upper and lower chambers to communicate with each other so they can function in a coordinated fashion.
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