Name the three main phases of the cardiac cycle in order and their key events.

Name the three main phases of the cardiac cycle in order and their key events.

• A. Diastole; Atrial Systole; Ventricular Systole
• B. Atrial Systole; Diastole; Ventricular Systole
• C. Ventricular Systole; Atrial Systole; Diastole
• D. Atrial Systole; Ventricular Systole; Diastole

Answer: (D)

The three main phases are atrial systole, ventricular systole, and diastole. In atrial systole, the atria contract to push the remaining blood into the ventricles; the atrioventricular valves are open and the semilunar valves are closed, so no blood leaves the heart yet. When the ventricles begin to contract, the AV valves close to prevent backflow (producing the first heart sound) and the semilunar valves open, allowing blood to be ejected into the aorta and pulmonary trunk. After the peak of contraction, the ventricles relax and the semilunar valves close (producing the second heart sound), marking the start of diastole; the AV valves reopen and the ventricles fill, first passively and then with the atrial contraction helping to top off ventricular volume at the end of diastole.

The three main phases are atrial systole, ventricular systole, and diastole. In atrial systole, the atria contract to push the remaining blood into the ventricles; the atrioventricular valves are open and the semilunar valves are closed, so no blood leaves the heart yet. When the ventricles begin to contract, the AV valves close to prevent backflow (producing the first heart sound) and the semilunar valves open, allowing blood to be ejected into the aorta and pulmonary trunk. After the peak of contraction, the ventricles relax and the semilunar valves close (producing the second heart sound), marking the start of diastole; the AV valves reopen and the ventricles fill, first passively and then with the atrial contraction helping to top off ventricular volume at the end of diastole.