→Fig. 1-2. Heart chambers and valves. There are four heart valves. The two atrioventricular valves (mitral and tricuspid) lie between the atria and the ventricles, and the aortic and pulmonic valves lie between the ventricles and their outflow vessels (aorta and pul monary artery). During systole, the ventricles con tract, fo rcefully expelling blood into the outflow vessels; while this occurs, the atrioventricular valves prevent backflow of this blood from the ventricles to the atria. During diastole, the ventricles relax and fill with blood from the atria; while this occurs, the aortic and pulmonary valves prevent backflow of the blood that has just been ej ected during systole. Mnemonic for the atrioventricular (AV) valves: The tricuspid is on the right. The mitral is on the left.
