The characteristics of regional and global left ventricular dysfunction due to isolated left circumflex (LC) artery stenosis were determined from the contrast ventriculograms of 52 patients studied during acute myocardial infarction. In patients with a left dominant coronary circulation (35%), the severity, circumferential extent and location of hypokinesia resembled those of right coronary artery stenosis. However, in patients with a right dominant or balanced circulation (65%), the location of LC artery-related hypokinesia varied over the entire left ventricular contour, overlapping with the territories of the left anterior descending and right coronary arteries. The method for measuring the severity of hypokinesia was adjusted to take into account the wide territory of the LC artery. This enhanced the sensitivity of the method, particularly in the right anterior oblique view, as indicated by the greater severity of hypokinesia measured (-2.5 +/- 0.9 vs -1.8 +/- 1.1 standard deviations by our previously published method, p less than 0.001). However, the overlap of the artery territories may make it difficult to selectively measure the dysfunction due to stenosis of an artery of interest in patients with multiple infarctions. The circumferential extent of hypokinesia due to LC artery thrombosis was greater in the left than the right anterior oblique view. When averaged over both views, the size of the dysfunctional segment approached that due to left anterior descending coronary artery thrombosis, exceeding the size previously reported. These results suggest that current eligibility criteria for thrombolytic therapy select patients with extensive LC artery beds.