A total of 107 consecutive patients with acute myocardial infarction underwent emergency coronary angioplasty (PTCA). Restoration of blood flow with TIMI grade III was established by emergency PTCA in 101 patients (94.4%). "Acute restenosis" was defined as a lesion that, when dilated to less than 50%, narrowed again to more than 75% luminar reduction 5 min after the balloon inflation. Acute restenosis occurred in 39 patients (39%). Multivariate analysis selected 3 factors associated significantly with an increased rate of acute restenosis: (1) dissection, (2) small balloon/artery diameter ratio and (3) low systolic blood pressure during PTCA. Reocclusion, which was defined as a total reobstruction of the lesion during hospitalization following emergency PTCA, was examined by predischarge coronary angiography. Acute restenosis correlated significantly with an increase in reocclusion rate. The incidence of documented reocclusion was 12%. Residual stenosis, multivessel disease and irregular dilation correlated significantly with an increased rate of reocclusion. The in-hospital and postdischarge mortalities were 5.6% and 2.1%, respectively. In summary, emergency PTCA produced a high angiographic success rate. Use of adequate balloon size and sufficient dilation correlated significantly with angiographic outcome in emergency PTCA. Patients with acute restenosis, high residual stenosis, irregular dilation, and multivessel disease would have a relatively high risk of reocclusion.