The prevalence and prognostic value of ventricular arrhythmias were examined in 45 Duchenne muscular dystrophy patients without congestive heart failure and followed up for 3 yr. Baseline evaluation included 24 h ECG monitoring, systolic time intervals measurement (preejection period/left ventricular ejection time PEP/LVET), echocardiogram and vital capacity tests. Fifteen patients (33%) had ventricular premature beats (VPB > or = 2 h-1). More complex ventricular ectopy (Lown grades 3, 4A, 4B) occurred in 12 patients (27%), who had abnormal ventricular contractility (PEP/LVET > 0.48) and an area of akinesia or dyskinesia. Complex VPB were present on presentation in only 3 of the 30 survivors (10%) but were detected in 6 of the 15 patients (40%) who died. Patients who died suddenly were more likely to have had documented complex ventricular arrhythmias (6 of 9; 66%). It is concluded that: (1) significant arrhythmias frequently coexist with asymptomatic left ventricular dysfunction and wall motion abnormalities; (2) complex VPB as well as left ventricular dysfunction and dilated cardiomyopathy are risk factors for sudden death.