Analysis of beat to beat changes in left ventricular (LV) ejection time during cardiac pacing was utilized to assess the atrial contribution to ventricular filling in coronary artery disease. The recordings of aortic pressure were made during atrial and ventricular pacing at a rate of 5 to 10 beats/min above sinus rhythm. During ventricular pacing, LV ejection time became maximum when an atrial contraction preceded a ventricular contraction by a physiologic interval and was similar to that obtained during atrial pacing (max ET). When the atrial systole occurred with or followed the paced ventricular contraction, LV ejection time became minimum (min ET). The atrial contribution was calculated as (max ET--min ET)/max ET X 100(%). Patients with coronary artery disease had a significantly large atrial contribution. In patients without myocardial infarction, the atrial contribution was increased to compensate for impaired early diastolic filling. In patients with myocardial infarction, the atrial contribution was reduced when LV end-diastolic pressure was markedly high. The atrial contribution generally plays an important role in increasing stroke volume, but it had less effect despite the forceful atrial contraction as LV filling pressure became more elevated.