To determine whether the initial degree of coronary narrowing prior to a first myocardial infarction (MI) affects left ventricular function, we analyzed paired coronary angiograms and left ventriculography in 41 consecutive MI patients in whom coronary angiography was obtained before and after MI. Patients were divided into 2 groups according to coronary narrowing of the infarct culprit lesion at first angiogram; a significant narrowing group (group S, 15 patients) and a nonsignificant narrowing group (group N, 26 patients). Significant narrowing was defined as more than 75% stenosis of an infarct-related segment in the first angiography and nonsignificant narrowing was less than 50% narrowing. Clinical characteristics were similar in the two groups, with the exception of initial diameter stenosis. LV function was normal in both groups at initial examination. Group S patients had a higher prevalence of angina prior to MI (73% versus 23%; P = 0.001), good collateral development (73% versus 35%; P = 0.02), and non-Q MI (73% versus 27%; P = 0.004) than group N patients. RWM was also superior in group S compared with group N. The deterioration of global and infarction zone function was mild in group S compared with group N (group S; median EF -10%, RWM -0.27 SD/chord, group N; median EF -26%, RWM -1.62 SD/chord, P = 0.001). We conclude that deterioration of LV wall motion in patients with severe stenosis in their initial stenosis would be milder than in AMI that developed from a mild degree of stenosis.