Four chambers

The heart has two atria above and two ventricles below. The right side receives deoxygenated blood from the body and pumps it to the lungs. The left side receives oxygenated blood from the lungs and pumps it to the body. The septum separates the sides and prevents mixing.

Valves

Atrioventricular valves lie between atria and ventricles. Semilunar valves lie at the bases of the pulmonary artery and aorta. Valves open when pressure behind them is greater and close when pressure in front becomes greater. They do not actively open and close by muscle contraction.

Muscular wall

Cardiac muscle contracts rhythmically without tiring under normal conditions. The left ventricular wall is thickest because it must create high pressure for the systemic circuit. The right ventricular wall is thinner because the lungs are nearby. Atrial walls are thinnest because they only push blood into ventricles.

Coronary arteries

The heart muscle needs its own supply of oxygen and glucose. Coronary arteries branch from the aorta and run over the heart surface. Narrowing or blockage reduces aerobic respiration in cardiac muscle and may cause angina or a heart attack.

Orientation in diagrams

Diagrams are often viewed from the front, so the anatomical right side appears on the left of the page. Do not identify chambers only by position. Follow the connected vessels: vena cava enters the right atrium, pulmonary vein enters the left atrium, pulmonary artery leaves the right ventricle and aorta leaves the left ventricle.

Review questions and suggested answers