Determination of left ventricular performance by external STI was evaluated in 113 patients with possible coronary artery disease undergoing selective coronary artery disease undergoing selective coronary arteriography and left ventriculography. Angiographically determined significant coronary artery disease was considered as 70 per cent obstruction of a coronary vessel. PEPI and PEP/LVET increased with increasing severity of coronary artery disease. LVETI decreased with increasing coronary artery involvement. Presence of prior myocardial infarction or clinically apparent congestive heart failure did not significantly alter mean STI values when groups were compared according to severity of coronary artery disease. LVETI was significantly less for patients with three-vessel coronary artery disease than for those with no significant disease; PEPI and PEP/LVET were significantly greater in those with two- or three-vessel disease than in those without significant disease. Angiographically determined LVEF correlated directly with LVETI and inversely with PEPI and PEP/LVET. Abnormal left ventricular wall motion was associated with decreased LVETI and increased PEPI and PEP/LVET. LVEDP was not significantly different in any of the groups. These findings indicate that externally determined systolic time intervals reflect abnormalities in left ventricular performance which in turn appear more pronounced with increasingly extensive coronary artery disease.