How does an increase in heart rate affect diastolic filling time?

How does an increase in heart rate affect diastolic filling time?

• A. Increases diastolic filling time
• B. No effect on diastolic filling time
• C. Slightly increases diastolic filling time, preserving preload
• D. Shortens diastole and reduces diastolic filling time, potentially decreasing preload

Answer: (D)

An increased heart rate shortens the diastolic phase, the period when the ventricles fill. With less time for filling, the ventricle ends diastole with less blood—so end-diastolic volume and preload decrease. This reduced preload can in turn lower stroke volume via the Frank-Starling mechanism, even though the heart is beating faster. Higher rates do not increase diastolic filling time, and while atrial contraction can help a bit, the overall effect is a shorter diastolic filling window and potentially reduced preload.

An increased heart rate shortens the diastolic phase, the period when the ventricles fill. With less time for filling, the ventricle ends diastole with less blood—so end-diastolic volume and preload decrease. This reduced preload can in turn lower stroke volume via the Frank-Starling mechanism, even though the heart is beating faster. Higher rates do not increase diastolic filling time, and while atrial contraction can help a bit, the overall effect is a shorter diastolic filling window and potentially reduced preload.