Digital M-mode echocardiography describes a characteristic alteration in the pattern of left ventricular filling when a dilated cardiomyopathy is present. The peak rates of early diastolic dimension change (dD/dt and dD/dt/D) are uniformly reduced but remain unchanged in time of occurrence (time to dD/dt). The rapid filling period is slightly shortened compared to normals, but the %deltaD taking place during rapid filling is not different than normals. This pattern is distinct from characteristic alterations seen in other cardiac diseases that have preserved systolic performance. While M-mode indices of left ventricular filling may be altered by several factors, the most significant factors in dilated cardiomyopathy are the severity of systolic dysfunction and preload. Left-sided conduction delays and associated right ventricular enlargement have no demonstrable effect on very early portions of diastole, but the conduction delay does prolong the rapid filling period and reduce the extent of filling during this period. Combined use of digitized M-mode echocardiograms and Doppler analysis of transmitral flow may allow a more complete description of left ventricular filling in future studies.