During which phase does the heart muscle relax and fill with blood?

During which phase does the heart muscle relax and fill with blood?

• A. Systole
• B. Diastole
• C. Plateau
• D. Tachycardia

Answer: (B)

Relaxation and filling of the heart chambers occur during diastole. In this phase the ventricles relax after contracting, allowing pressure to fall and the atrioventricular valves to open so blood flows from the atria into the ventricles. Filling happens both passively and, toward the end of diastole, due to atrial contraction that pushes in the remaining blood. This sets the ventricles up for the next contraction. Systole is the contraction phase that pumps blood out of the ventricles. The plateau refers to a stage of the cardiac action potential, not a filling phase. Tachycardia describes a fast heart rate, which can alter diastolic filling time but is not the phase of relaxation and filling itself.

Relaxation and filling of the heart chambers occur during diastole. In this phase the ventricles relax after contracting, allowing pressure to fall and the atrioventricular valves to open so blood flows from the atria into the ventricles. Filling happens both passively and, toward the end of diastole, due to atrial contraction that pushes in the remaining blood. This sets the ventricles up for the next contraction. Systole is the contraction phase that pumps blood out of the ventricles. The plateau refers to a stage of the cardiac action potential, not a filling phase. Tachycardia describes a fast heart rate, which can alter diastolic filling time but is not the phase of relaxation and filling itself.