During bradycardia, how does it affect the duration of diastole and ventricular filling time?

During bradycardia, the heart beats more slowly, which inherently increases the length of diastole—the phase of the cardiac cycle when the heart muscle relaxes and the chambers fill with blood. This extended diastolic period means that there is a longer time for ventricular filling compared to a normal or fast heart rate.

With an increase in diastolic duration, the ventricles have more time to fill with blood from the atria, which consequently raises the volume of blood in the ventricles at the end of diastole. This increase in ventricular filling volume effectively enhances preload, which is the strain on the ventricular wall at the end of diastole before contraction. A higher preload can lead to a more forceful contraction based on the Frank-Starling mechanism, where the heart pumps more efficiently with increased venous return.

Therefore, during bradycardia, the longer duration of diastole increases preload, supporting the correct answer.