Aging is the primary cause of diastolic heart failure, also called diastolic dysfunction. With time, the heart muscle becomes too stiff, preventing the heart from filling with blood properly. High blood pressure, narrowed opening of the aortic valve, coronary artery disease and pericardial disease all affect the left heart ventricle during diastole, notes WebMD.
Diastole is the heartbeat phase that occurs when the heart relaxes, allowing the blood to fill the left ventricle, states WebMD. Diastolic heart failure occurs when the ventricles become stiff or do not relax properly, causing an insufficient amount of blood to enter the heart, according to MedicineNet.
When the left ventricle thickens or becomes stiff, the heart must apply more pressure than normal inside the heart chamber to make the blood fill the ventricle. If this condition continues, the blood builds up in the lungs, causing fluid congestion and heart failure, explains WebMD.
Diastolic dysfunction might not affect the ejection fraction, which is the amount of blood that the heart pumps out divided by the amount of blood that the left ventricle holds, notes WebMD. This fraction may be lower in patients with systolic heart failure, a condition in which the heart muscles do not contract with enough force.