This study examined the incidence of cardiac conduction abnormalities and ventricular arrhythmias after the transcatheter closure of muscular ventricular septal defects (MVSDs) using the Amplatzer device occluder. From the records of 27 patients who underwent 33 consecutive MVSD device closures, a low incidence of permanent and transient cardiac conduction disturbances was observed. Heart rate variability was less after the closure of multiple MVSDs compared with single MVSDs.