Myocardial ischaemia affects left ventricular relaxation. The velocity of propagation of rapid left ventricular filling flow (VPF, cm/s) measured by colour M-mode is strongly correlated with the haemodynamic constant of left ventricular relaxation (Tau). The authors compared the changes in VPF during stress echocardiography with Dobutamine in a control group of non-coronary patients (Group 1, N = 12) and a group of coronary patients (Group 2, N = 29). Coronary angiography was performed in all patients. The basal VPF were similar in both groups (Group 1: 68.3 +/- 22.7 cm/s vs Group 2: 66.2 +/- 23.1 cm/s, NS). The VPF at the peak of dobutamine infusion were significantly different from the values observed under basal conditions in Group 1 (105.1 +/- 25.0 cm/s, p < 0.001) whereas this difference was not significant in Group 2 (67.4 +/- 19.3 cm/s, NS). There were significant differences between the two groups for peak values (p < 0.001) and for percentage variation of VPF (peak-basal value/basal value) with respect to the basal values (Group 1: 63 +/- 43% vs Group 2: 9 +/- 39%, p < 0.01). A percentage variation of VPF < 25% (Group 1: 3/12 patients and Group 2: 23/29 patients) allows detection of coronary artery disease with a sensitivity of 79% and a specificity of 75%. During Dobutamine infusion, the velocity of propagation of left ventricular filling flow increases less in coronary patients than in non-coronary patients. The study of this quantitative parameter of left ventricular relaxation seems to be a valuable tool for detecting the presence of coronary artery disease during stress echocardiography.