diastolic function
Diastolic function is how well the heart relaxes and refills between beats — the receiving half of the pump. A good pump must not only squeeze well but also loosen and accept blood easily, the way a sponge must expand to soak up water again.
Good diastolic function means the ventricle relaxes quickly and stays supple, so it fills with blood at low pressure. Relaxation is an active, energy-using process, not mere passive recoil, and the chamber's stiffness then governs how easily it accepts blood.
When relaxation is slow or the muscle is stiff, the ventricle fills only at higher pressures, which back up into the lungs and cause breathlessness — this is diastolic dysfunction. It can exist even when the squeeze (ejection fraction) looks completely normal, underlying heart failure with preserved ejection fraction.
Diastolic function is assessed mainly with Doppler echocardiography, looking at the speed of blood flowing into the ventricle and the speed at which the heart muscle relaxes. It tends to worsen with age, high blood pressure, thickened muscle, and diabetes.
An older patient with long-standing hypertension and a thickened, stiff left ventricle may become breathless on exertion despite a normal ejection fraction — a hallmark of impaired diastolic function.
Stiff, poorly relaxing ventricles can cause symptoms even with normal ejection fraction.
Diastolic function is the relaxation-and-filling counterpart to systolic function (the squeeze). Both can fail independently; a heart can pump strongly yet fill poorly, or vice versa.