Why does the length of diastole change with exercise?

During exercise, the heart rate increases, leading to a shorter duration of diastole, which is the phase when the heart relaxes and fills with blood. As the heart beats more rapidly, there is less time for the chambers to fill completely between beats. Additionally, the body's demand for oxygen and nutrients rises, prompting the heart to pump more efficiently, often resulting in a reduced diastolic time to maintain adequate blood flow.