Anatomy of the human heart

The heart is a big muscular pump that operates throughout life, pumping blood through the body's dual circulation (pulmonary and systemic). It lies in the mediastinum in the chest, sort of between the anterior chest wall and the lungs.

The human heart is surrounded by a thin layer of tissue known as the pericardium and the space between the heart and pericardium is filled with a small amount of pericardial fluid. The human heart is made up of four chambers. The right atrium receives deoxygenated blood from the body via the superior vena cava and the inferior vena cava. This blood passes to the right ventricle, where it is pumped out along the pulmonary arteries to the lungs. Oxygenated blood returns to the heart from the lungs via the pulmonary veins which end in the left atrium. This blood is pumped to the left ventricle and is then pumped into the systemic circulation through the aorta.

In the normal heart, the walls of the ventricles are thicker than those of the atria and the wall of the left ventricle is thicker than the wall of the right ventricle (the left ventricle must pump blood to the entire body).

There are four valves in the heart. The tricuspid valve separates the right atrium from the right ventricle. The pulmonary valve prevents backflow from the pulmonary artery into the right ventricle. The mitral valve (also known as the bicuspid valve) separates the left atrium from the left ventricle. Finally, the aortic valve prevents backflow of blood from the aorta into the left ventricle and therefore helps keep the systemic blood pressure up.

A continuous septum separates the left and right atria and the left and right ventricles.

Blood supply to the heart arises via two blood vessels that branch off early from the aorta, namely the left coronary artery and the right coronary artery. The left coronary artery branches into the left anterior descending artery and the left circumflex artery. The right coronary artery sends an important branch to the SA node in the right atrium. Occasionally, anatomical variants of the coronary arteries are found and these can vary quite widely in pattern.

The heart is innervated by autonomic fibres, both sympathetic and parasympathetic (from the vagus nerve) and is also affected by the volume of venous return to the heart and to hormones such as adrenaline.

Part of the human anatomy project.