A large number of patients suspected of having congestive heart failure have normal left ventricular systolic function and may, therefore, have primary diastolic heart failure. This diagnosis, however, should not be made unless there is also objective evidence of diastolic dysfunction, ie, signs of abnormal left ventricular relaxation and/or diastolic distensibility. The most useful noninvasive diagnostic approaches are the measurement of transmitral and pulmonary venous flow velocities by pulsed wave Doppler, and mitral annulus velocities by tissue Doppler echocardiography. In some patients, the assessment of intraventricular flow propagation by colour M-mode Doppler echocardiography provides additional information. Diastolic heart failure is most often due to coronary artery disease and/or hypertension; therefore, other noninvasive or invasive tests are needed to define the etiology of myocardial dysfunction. However, in the few patients who have constrictive pericarditis, the Doppler echocardiographic assessment of diastolic filling provides the most important clues to the etiology of the disease. Doppler echocardiographic assessment of left ventricular filling may also be used to obtain semiquantitative estimates of left ventricular diastolic pressure. Furthermore, left ventricular filling patterns, in particular, the deceleration time of early transmitral filling, are powerful predictors of patient prognosis. It is probably not cost effective to perform a comprehensive assessment of diastolic filling in every patient undergoing an echocardiographic examination. However, in selected patients, the assessment of diastolic filling provides information that is important for patient management.