Which are the three stages of the cardiac cycle?

• A. Atrial systole, ventricular systole, diastole
• B. Atrial systole only
• C. Ventricular systole only
• D. Diastole only

Answer: (A)

The main idea here is understanding the three phases that make up a heartbeat: atrial contraction to push blood into the ventricles, ventricular contraction to eject blood into the circulation, and the relaxation/filling phase that follows. Atrial systole is when the atria squeeze blood into the ventricles, finishing the filling. Ventricular systole is when the ventricles contract to send blood out to the lungs and body. Diastole is the period of relaxation when the heart chambers fill again in preparation for the next beat. Together, these three stages describe the complete cycle of one heartbeat. The other options are incomplete because they mention only a single phase and omit the others.