Final answer:
Tachycardia decreases the duration of diastole and ventricular filling time, reducing the preload. The heart's reduced filling time leads to a lower end diastolic volume, which means the preload decreases despite mechanisms to compensate for rapid heart rates.
Step-by-step explanation:
Tachycardia will decrease the duration of diastole & ventricular filling time, subsequently reducing preload. During tachycardia, the heart beats more rapidly, which shortens the time ventricles have to fill with blood during diastole. As the duration of ventricular diastole decreases, there is less time for ventricular filling, leading to a lower end diastolic volume (EDV) and hence a lower preload. Although contractility, representing the force of heart contractions, can initially help sustain the stroke volume (SV), over time the heart often cannot fully compensate for the reduction in filling time, and thus preload is reduced.