when are av valves closed in cardiac cycle
Cardiac cycle The mitral and tricuspid valves, also known as the atrioventricular, or AV valves, open during ventricular diastole to permit filling. Late in the filling period the atria begin to contract (atrial systole) forcing a final crop of blood into the ventricles under pressureâ€”see cycle diagram. Then, prompted by electrical signals from the sinoatrial node, the ventricles start contracting (ventricular systole), and as back-pressure against them increases the AV valves are forced to close, which stops the blood volumes in the ventricles from flowing in or out; this is known as the isovolumic contraction stage.[4]
Chordae tendineae When the ventricles of the heart contract in ventricular systole, the increased blood pressures in both chambers push the AV valves to close simultaneously, preventing backflow of blood into the atria. Since the blood pressure in atria is much lower than that in the ventricles, the flaps attempt to evert to the low pressure regions. The chordae tendineae prevent the eversion, prolapse, by becoming tense thus pulling the flaps, holding them in closed position.[1]