Incidence and type of premature ventricular contractions (PVC) were studied by ambulatory monitoring in 66 patients at the average 20 months after left ventricular aneurysmectomy. In 25 of these patients long-term-Ecg-monitoring was obtained before and after surgical intervention. After aneurysmectomy only 30% of all patients showed no PVCs; 35% had few PVCs and 35% demonstrated frequent PVCs. In 16 patients (24%) PVCs of Lown Classes III and IV were found. Only 7 out of 25 patients of the group analyzed before and after aneurysmectomy improved by one or more Lown Classes, 10 patients remained in the same Class, 8 patients worsened. In 11 patients ventricular arrhythmias refractory to medical treatment were the indication for aneurysmectomy. There were three in-hospital deaths. Of the remaining 8 patients only two became free from ventricular ectopic activity, 5 continued to have frequent multifocal PVCs, two of them required repeatedly DC-cardioversions. In two patients sudden cardiac death occurred two and three years after aneurysmectomy. It is concluded that only a small percentage of patients with left ventricular aneurysm gets free from ventricular ectopic activities after aneurysmectomy. Results of aneurysmectomy for intractable ventricular arrhythmias are disappointing and unpredictable. The application of new surgical techniques to localize and excise irritable foci seems advisable for the future.