Abnormalities of diastolic function have a major role in producing the signs and symptoms of heart failure. However, diastolic function of the heart is a complex sequence of multiple interrelated events, and it has been difficult to understand, diagnose and treat the various abnormalities of diastolic filling that occur in patients with heart disease. Recently, Doppler echocardiography has been used to examine the different diastolic filling patterns of the left ventricle in health and disease, but confusion about diagnosis and treatment options has arisen because of the misinterpretation of these flow velocity curves. This review presents a simplified approach to understanding the process of diastolic filling of the left ventricle and interpreting the Doppler flow velocity curves as they relate to this process. It has been hypothesized that transmitral flow velocity curves show a progression over time with diseases involving the myocardium. This concept can be applied clinically to estimate left ventricular filling pressures and to predict prognosis in selected groups of patients. Specific therapy for diastolic dysfunction based on Doppler flow velocity curves is discussed.