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INTRODUCTION: Clinical studies have shown that approximately 40% of patients with congestive heart failure have predominantly diastolic left ventricular dysfunction. Doppler echocardiography is a simple, noninvasive and safe technique that can be used for measurement of diastolic filling and, therefore for assessment of diastolic function. PHYSIOLOGY OF DIASTOLE: Diastole is divided into four phases: isovolumetric relaxation, rapid filling, slow filling (diastasis) and atrial contraction. Diastolic filling can be defined as the period from the onset of mitral valve opening to mitral valve closure. DETERMINANTS OF DIASTOLIC FILLING: The two major determinants of diastolic filling are ventricular relaxation (characterized by the rate and duration of the decrease of left ventricular pressure after systole) and compliance (defined by volume changes over the change in pressure during diastolic filling). NORMAL TRANSMITRAL FLOW PATTERN: When pulsed Doppler sample volume is placed at the tips of mitral leaflets, recorded transmitral velocity pattern is composed of two principal deflections: the E wave, occurring during the rapid filling phase, and the lower A wave, arising from atrial contraction. These two waves are usually separated with relatively low velocity signal during diastasis. Numerous indices derived from this pattern have been proposed as markers of diastolic function (peak and integrated velocities of the E and A waves, their ratio, and acceleration and deceleration times of the E wave). However, it should be noted that these indices, in fact, measure diastolic filling, rather than function. Even in healthy individuals, numerous factors may have impact on transmitral flow pattern, including age, heart rate, loading conditions and filling pressures. NORMAL PULMONARY VENOUS FLOW PATTERN: Analysis of pulmonary venous flow pattern (obtained by pulsed Doppler sample volume placed in pulmonary vein) gives additional information and may help in the assessment of left ventricular filling. Usually, three distinct velocity waves can be observed: S wave, occurring during ventricular systole; 1) wave, diastolic wave that begins after mitral wave opening: and finally, AR wave, reversal velocity during atrial contraction. When diastolic filling is altered, typically there is an inverse relationship between transmitral E and pulmonary venous S wave, as well as transmitral A and pulmonary venous D wave. PATHOLOGIC FILLING PATTERNS: There are three different pathologic filling patterns: 1) delayed (prolonged, impaired) relaxation pattern, characterized by prolonged isovolumetric relaxation time and deceleration time, low E and high A wave velocities with an E/A wave ratio typically 1; 2) restrictive pattern, associated with shortened isovolumetric relaxation time, increased peak E wave velocity with very short deceleration time, and small (or even absent) A wave, leading to an E/A wave ratio 2; and 3) pseudonormal pattern, usually an intermediate stage between delayed relaxation and restrictive filling, as a consequence of disease progression; it may be unmasked by Valsalva maneuver and is characteristically associated with atrial dilatation and prominent pulmonary venous AR reversal. CLINICAL APPLICATIONS: Impaired diastolic function is frequently the first detectable abnormality in many of cardiac diseases. With serial recordings, changing of filling patterns, from delayed relaxation, through pseudonormalization, and, finally, to restrictive filling pattern can be observed. These changes have been demonstrated to correspond well with progression of cardiac diseases. According to the severity of symptoms and transmitral filling pattern, four-grade model of diastolic dysfunction has been proposed. It has been shown that the E/A ratio 2 and deceleration time 150 ms indicate poor prognosis in patients with dilated cardiomyopathy, cardiac amyloidosis and old myocardial infarction, independently of the severity of systolic dysfunction. (ABS