Heart failure with a normal ejection fraction is interchangeably termed diastolic heart failure. This condition is often unrecognized and it does have diagnostic, prognostic and therapeutic implications that are distinct from those conditions with systolic dysfunction. It is clinically important to understand and assess the diastolic function to reliably manage the patients suffering with heart failure. With the results of randomized trials for this distinct clinical syndrome, as well as the probability of better diagnostic testing in the future, physicians will in a better position not only to diagnose diastolic dysfunction or heart failure, but also to manage it more effectively. In this review, the physiology of the diastole and how to evaluate the abnormalities of the diastolic function will be discussed.