BACKGROUND: In Duchenne muscular dystrophy (DMD), cardiac causes account for approximately 30% of all deaths. Therefore, evaluating cardiac function in older patients is important. In addition, current recommendations advise screening for arrhythmias when left ventricular dysfunction is identified; however, the evidence base underpinning this recommendation in DMD is limited. Furthermore, large-scale cohort studies with substantial adult representation are lacking. METHODS: To characterize arrhythmia profiles of patients with DMD, we analyzed 1018 Holter electrocardiographic recordings from 167 patients with DMD (age: 9-44 years). RESULTS: Bradyarrhythmia and supraventricular tachyarrhythmia were rare; nonsustained ventricular tachycardia (NSVT) and ≥ 720 premature ventricular complexes per 24 h were detected in 85 (8.3%) and 124 (12.2%) recordings, respectively. Logistic regression identified reduced left ventricular function as the strongest associated factor for NSVT. Although statistically nonsignificant, risk increased with age, nonuse of noninvasive positive-pressure ventilation, and a Dp140-deficient genotype. A Dp116-deficient genotype was associated with lower odds of NSVT. CONCLUSIONS: Given that NSVT may trigger sudden cardiac death in susceptible patients with underlying cardiac disease, regular Holter electrocardiographic monitoring is warranted in patients at high risk of NSVT.