AEMCA Practice Exam

During which phase do the atrioventricular valves open?

1. Systole

2. Diastole

3. Isovolumetric contraction

4. Cardiac output

The correct answer is: Diastole

The atrioventricular valves open during diastole, which is the phase of the cardiac cycle when the heart muscle relaxes. This relaxation allows the ventricles to fill with blood from the atria. During diastole, the pressure in the atria exceeds that in the ventricles, causing the atrioventricular valves (the mitral and tricuspid valves) to open, facilitating the flow of blood into the ventricles. In contrast, during systole, the heart is contracting and the ventricles are ejecting blood into the arteries. The atrioventricular valves close at this time to prevent backflow of blood into the atria. Isovolumetric contraction occurs at the beginning of systole when the ventricles contract but there is no change in volume because the valves are closed, further highlighting why this phase does not involve the opening of the atrioventricular valves. Cardiac output refers to the amount of blood the heart pumps in a given time and is not a phase of the cardiac cycle itself.