Two patients who had sudden unexpected death while being monitored by a Holter electrocardiograph apparatus are reported. The first patient with heart disease of unknown etiology initially developed first degree A-V block, progressive left bundle branch block and finally asystole. The second patient with previous coronary artery disease and recent myocardial infarction revealed multifocal ventricular extrasystoles with frequent bigeminism and trigeminism which ended in ventricular tachycardia and fibrillation. Emphasis is made on the necessity of detecting those high risk patients and establishing preventive post-hospitalization care to modify the evolution and prognosis in this group of patients.