The parameters of myocardial function in the initial phase of ventricular ejection are theoretically more sensitive than the indices calculated over the total systolic ejection period. The object of this study was to evaluate whether the calculation of the ejection fraction by thirds of systole, giving a separate assessment of left ventricular performance at the beginning, the middle and end of ejection, could reliably detect minor changes in ventricular function unrecognised by the usual holosystolic indices. Seventy left ventricular angiograms were analysed in 20 normal subjects (Group I) and 50 patients with coronary artery disease whose ventricular function estimated by the usual parameters was either decreased (Group II, 20 patients) or normal (Group III, 30 patients). In Group I, the ejection fraction in the first third of systole (FE1/3) was much higher than the ejection fraction in the second third (FE2/3). On the other hand, in Groups II and III, all patients had a FE1/3 lower than the FE2/3 (specificity: 100 p. 100). In these two groups, the reduction of FE1/3 and the increase of FE2/3 were very significant compared to Groupe I (p less than 0,001). The ejection fraction of the lest third was identical in the 3 groups. This abnormal distribution of ejection was detected in all coronary patients and was the only alteration of ventricular performance in each of the 30 patients in Group III. In this group, this abnormality was detected equally in patients with triple vessel disease (Subgroup III a, 20 patients) and in patients with isolated left anterior descending disease (Subgroup III b, 10 patients) illustrating the high sensitivity of this index for the detection of a minor abnormality of myocardial function.