It remains controversial whether percutaneous transluminal coronary angioplasty (PTCA) performed 24 hours after the onset of acute myocardial infarction (AMI) in coronary arteries with 99% stenosis is useful in preserving left ventricular function. We investigated the effectiveness of PTCA in preventing left ventricular remodeling when it was performed 24 hours after the onset of AMI in infarct-related coronary arteries (IRCAs) having 99% stenosis and thrombolysis in myocardial infarction (TIMI) grade 3 flow. The subjects were 19 patients with AMI (anterior wall, 9 patients; inferior wall, 7 patients; and non-Q, 3 patients) who, within 24 hours of the onset of AMI, underwent coronary angiography and left ventriculography during the acute and/ or chronic phases. The patients were divided into a PTCA group, comprised of patients in whom PTCA was successfully performed 24 hours after the onset of AMI (n = 10), and a non-PTCA group (n = 9). The non-PCTA group included patients who were successfully reperfused by thrombolysis and did not include patients who had spontaneous reperfusion or reperfusion after PTCA. In the non-PTCA group, the left ventricular end-diastolic volume (mean +/- SD) was significantly increased in the chronic phase (86 +/- 23 mL/m(2)) as compared with the acute phase (67 +/- 13 mL/m(2)), whereas in the PTCA group no significant difference was observed between end-diastolic volumes in the acute and chronic phases (67 +/- 26 and 68 +/- 13 mL/m(2), respectively). Left ventricular remodeling is prevented by PTCA when it is performed 24 hours after the onset of AMI in IRCAs with 99% stenosis and TIMI grade 3 flow.