In recent years, there has been increased recognition of the relative importance of abnormalities of diastolic function in patients with essential hypertension. Indeed, diastolic dysfunction may be the earliest indicator of hypertensive heart disease. In this article, the mechanisms governing normal ventricular relaxation and the factors that may cause diastolic dysfunction are reviewed. Noninvasive clinical methods, particularly Doppler echocardiography and radionuclide angiography, for determination of diastolic function are outlined, and the limited experience in the management of hypertensive patients with abnormalities of diastolic function is discussed. When congestive heart failure develops in a patient with hypertension, it is especially important to determine whether it is due primarily to systolic or to diastolic left ventricular dysfunction.