A dilated left ventricle with reduced ejection fraction is usually attributed to impaired systolic function. To investigate the possibility that ventricular filling might also be disturbed, M mode echocardiograms, phonocardiograms, and Doppler cardiograms were recorded in 30 patients with ventricular disease of varying cause. All but four had functional mitral regurgitation. The size of the left ventricular cavity was increased in all and peak velocity of circumferential fibre shortening was reduced. Diastolic abnormalities included a short isovolumic relaxation time, and, on digitised M mode, a reduced rate of dimension increase and of posterior wall thinning. Although the timing of aortic valve closure was normal, mitral regurgitation persisted beyond it by 95 (35) ms and beyond mitral valve opening by 60 (40) ms. This reduced the effective filling time (the interval when the mitral valve was open and mitral regurgitation was absent) to less than 200 ms in seven patients. The effective filling time correlated closely with the RR interval, the regression equation indicating a reduction of 80 ms for each 100 ms fall in RR interval. It was also independently shortened by 2 ms a year with increasing age. The effective left ventricular filling time may thus be very short in patients with left ventricular cavity dilatation and functional mitral regurgitation. It is suggested that when diastolic function is also abnormal, this short filling time may physically limit ventricular inflow. Its close relation to heart rate might contribute to the therapeutic effect of beta blockade in such patients.