Emery-Dreifuss muscular dystrophy (EDMD) is a rare X-linked muscular dystrophy characterized by early contractures, progressive muscle weakness, and atrial arrhythmias. Recent reports suggest that there may be additional cardiac problems in affected males and that carrier females may also show ECG abnormalities. We restudied two large families with EDMD in order to determine the extent of these problems. We examined 10 affected males and interviewed 2 others. The 3 affected males less than 20 years old had no ECG changes. All affected men of 35 years or older had arrhythmias. One had more severe arrhythmias when asleep, indicating the usefulness of continuous 24-h ECG monitoring in the evaluation of males affected with EDMD. Two required pacemakers, 4 had already had a pacemaker placed, and 4 other affected men with pacemakers had died prior to this study. One affected man with a pacemaker developed ventricular bigeminy and another developed congestive heart failure. Thus of 10 affected males with pacemakers, 6 had additional cardiac symptoms and 4 have died. Males with EDMD may survive longer with a ventricular pacemaker, but this may increase the likelihood that they will develop cardiomyopathy and ventricular arrhythmias. Of 34 carrier females examined, 6 had arrhythmias typical of EDMD. Two required a pacemaker. The risk of arrhythmia increased with age. Results from one family should be extrapolated to another with caution, as there appears to be significant interfamilial variation. We suggest careful cardiologic follow-up of EDMD patients and regular cardiac evaluations for older carrier females.