Abnormalities of diastolic function play a major role in producing the signs and symptoms of heart failure. In patients with heart failure and reduced left ventricular systolic function, concomitant diastolic dysfunction is invariably present. In addition, it is now well established that as many as 40% to 50% of patients with well-documented episodes of heart failure have preserved systolic function. Doppler echocardiography provides one of the most useful clinical tools for assessing left ventricular diastolic function and can provide diagnostic and prognostic information. The Doppler assessment of diastolic function should be part of the routine echocardiographic evaluation of patients suspected of having heart failure. This review focuses on the use of Doppler echocardiographic techniques to assess diastolic function. The Doppler patterns of diastolic filling observed and their progression over time in patients with myocardial disease are described and related to changes in the physiology of diastolic filling. In addition, Doppler echocardiographic-guided treatment strategies for heart failure are discussed.