Abnormalities of diastolic function in the critically ill have been demonstrated to be associated with important intensive care outcomes such as mortality and ventilator weaning failure. The assessment of left ventricular (LV) diastolic function refers requires the analysis of the onset, pattern, and termination of left ventricular filling as determined by the time course and magnitude of the pressure gradient between the left atrium (LA) and LV. Echocardiographic two-dimensional and Doppler findings can provide an indirect assessment of the pattern of LV filling and LA–LV pressure gradients. Current guidelines suggest as a minimum the measurement of LA area and volume, mitral inflow velocities, mitral annular velocities, and tricuspid regurgitant flow velocity (as an indirect assessment of left atrial pressure). Other measurable parameters are also available (e.g. pulmonary venous inflow velocities, isovolumic relaxation time, Colour M-mode mitral propagation velocity) and these may help in identifying and characterizing diastolic dysfunction. Generally, however, they are more difficult to perform. Irrespective of the echocardiographic findings measured and the guidelines followed, there is a paucity of data that validates either the individual measures or the guidelines themselves in the critically ill.