Severe vascular complications are an inherent risk of percutaneous transluminal coronary angioplasty (PTCA). Data from 100 emergency aortocoronary bypass operations required after 2850 interventions (3.5%) were retrospectively analysed in order to identify factors that determine postoperative infarct size. Large infarctions were assumed if the patient died of cardiogenic shock (n = 12), if postoperative angiography demonstrated a decrease in left ventricular ejection fraction of more than 20% of if R-waves in the ECG decreased by more than 40% and a QRS-score increased by more than 5. According to these definitions, 29 patients experienced large infarctions, while 71 experienced no or only small infarctions. The following factors differentiated the two groups: age (58 vs 53 years, P = 0.008), pre-PTCA exercise work load (88 vs 118 Watts, P = 0.0001), exercise ischaemia score (2.7 vs 1.9, P = 0.045), degree of pre-PTCA stenosis (83 vs 86%, P = 0.03), coronary multivessel versus single vessel disease (60 vs 38%, P = 0.02), collaterals to the target vessel (10 vs 34%, P = 0.05), total vascular occlusion during PTCA (76 vs 56%, P = 0.035), and long duration of ischaemia after onset of the complication (253 vs 179 min, P = 0.012). Data from patients with large postoperative infarctions who survived ranged between those with no or small infarctions and those who died of cardiogenic shock. Higher age (P = 0.04), reduced exercise tolerance (P = 0.0004), absence of collaterals (P = 0.04), and duration of ischaemia until reperfusion (P = 0.001) were independent predictors of large postoperative myocardial infarctions.(ABSTRACT TRUNCATED AT 250 WORDS)