The Holter tapes of 61 patients (46 men, mean age +/- standard deviation 65 +/- 11 years) with sudden cardiac death while being monitored were analyzed. Thirty-eight patients were known to have coronary artery disease, 5 had cardiomyopathy, and 7 had aortic valve disease. Etiology remained unknown in 11 patients. Mean New York Heart Association functional class was 2.5 +/- 0.7. Thirty patients had received antiarrhythmic drugs and 32 had received digitalis. Sudden death occurred at rest in 73%. In the hours before death, repetitive ventricular arrhythmias were found in 50 patients (82%), with atrial fibrillation in 34%. Patients with bradyarrhythmic death (18%) had less complex ventricular activity compared to patients with tachyarrhythmic death (p less than 0.01). Lethal arrhythmias--monomorphic ventricular tachycardia, polymorphic ventricular tachycardia, torsades de pointes, primary ventricular fibrillation, and 1:1 conducting atrial tachycardia--were found in 26 (43%), 15 (25%), 5 (8%), 3 (5%), and 1 patient, respectively. The coupling interval of the final ventricular tachycardia correlated inversely with the initial frequency of ventricular tachycardia (p less than 0.05). For patients with tachyarrhythmic death, an increase of heart rate within the last 3 hours was noted (83 vs 89 beats/min, p less than 0.05). Ventricular premature complexes and the proportion of patients with greater than 2 couplets and greater than 2 triplets increased significantly only within the last hour before death.(ABSTRACT TRUNCATED AT 250 WORDS)