The study of left ventricular relaxation, filling pressure and their application into clinical medicine. Diastolic dysfunction is regarded as an early symptom of heart disease and often antedates clinical or echo evidence of systolic dysfunction. It also explains difference in clinical symptoms between patients with similar ejection fraction (EF). Diastolic dysfunction does not equal diastolic heart failure (HF) and not always reflect the clinical status of the patient. Diastolic dysfunction may have evidences of either impaired left ventricular (LV) relaxation or reduced restoring force or elevated diastolic stiffness. This chapter covers the echocardiographic assessment of diastolic function, valsalva maneuver, transmitral Doppler inflow, isovolumic relaxation time, tissue Doppler imaging, pulmonary venous Doppler flow, mitral inflow propagation velocity and hepatic vein Doppler, tissue Doppler echocardiographic time intervals, grades of diastolic dysfunction, myocardial deformation measurements, and clinical utility of diastolic dysfunction.