The Heart

The heart is below, muscular organ situated in the front of the chest, between the lungs. Approximately two thirds of its mess is situated to the left of the median plane.

The heart is surrounded by a double membrane which is called pericardium. It contains fluid which lubricates the heart. The heart is divided into a right half and a left half by a wall of tissue. Each half is divided again into an upper and lower comber, so that the heart consists of four chambers.

The upper chambers of the heart are called atria and the lower chambers are called ventricles. The right atrium and the right ventricle are connected by a valve, and so are the left atrium and left ventricle. Another valve is situated between the right ventricle and pulmonary artery, and a fourth between the left ventricle and the aorta. These are called the semilunar valve because they are shaped like crescent moons.