Cardiac cycle

Relationship between the heart sounds, muscle contractions, blood flow, position of the valves, and apex in one complete cardiac cycle (either of the right or left side of the heart).

(A) When the first sound is heard, the ventricles contract, the apex strikes the anterior chest wall, the auricular-ventricular (ie, tricuspid and mitral) valves close, the pulmonic and aortic valves open, blood is forced into the pulmonary artery and the aorta, the columnae carnae (ie, the muscular ridges or projections on the walls of ventricles) and cordae tendineae (ie, strong, fibrous connections between the valve leaflets and the papillary muscle) are in tension, and blood flows passively into the auricles from the veins.

(B) When the second heart sound (S2) is heard, pulmonic and aortic valves close, the ventricles relax, blood continues to flow passively into the auricles from the veins, the auricular-ventricular (ie, tricuspid and mitral) valves begin to open, and the apex recedes from the chest wall.

(C) Aortic and pulmonic valves remain closed, the auricular-ventricular (ie, tricuspid and mitral) valves open, and blood flows passively into the ventricles from the auricles and into the auricles from the veins.

(D) The auricles contract, the auricular-ventricular (ie, tricuspid and mitral) valves are thrown wide open, blood flows forcibly from the auricles into the ventricles, the ventricles distend, and the pulmonic and aortic valves remain closed. Then the cycle is repeated. (Source: Slade CB. Physical Examination and Diagnostic Anatomy. Philadelphia and London: W.B. Saunders Company, 1910. Public domain.)