What happens to ventricular filling time when the heart rate is extremely high?

• A. It increases.
• B. It remains unchanged.
• C. It becomes irregular.
• D. It decreases.

Answer: (D)

Ventricular filling time hinges on how long the heart spends in diastole, the filling phase. When the heart rate becomes extremely high, diastole shortens a lot, leaving less time for blood to flow from the atria into the ventricles. That means the ventricles don’t fill as completely, so filling time effectively decreases. Although the heart may try to compensate, the rapid rhythm limits the opportunity for passive filling and atrial contraction to contribute fully. So, despite the faster beat, the time available for filling is reduced.