Aim: Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are neuromuscular diseases associated with progressive cardiac dysfunction. This study aims to determine the early markers of their cardiac involvement. Materials and Methods: This retrospective study was conducted with 26 boys with DMD-BMD (study group) diagnosed with genetic analysis. Healthy controls were 44 age-matched boys evaluated with electrocardiography (ECG), ambulatory Holter monitoring, and echocardiography (ECHO) to obtain a sport license. Heart rate variability (HRV) (SDNN, SDANN, SDNN index, Rmssd, pNN50), ECG (Heart rate, V1R/S, corrected QT, QRS-T angle, and parameters associated with ventricular repolarization heterogeneity) and ECHO parameters (ejection and shortening fraction, peak early and peak late diastolic velocities, tricuspid annular plane systolic excursion) of children with DMD and BMD were compared with healthy controls. The study group was also divided into “ambulatory” and “non-ambulatory” subgroups and differences in terms of cardiological parameters were evaluated between these subgroups. Results: ECG revealed shorter PR and higher V1R/S in the study group than in the control group (p<0.003 and p<0.01). Heart rate was higher in the study group with ambulatory Holter monitoring (p<0.01). There was no significant difference in ECHO parameters. Lower HRV values were found in the ambulatory subgroup than in the non-ambulatory subgroup (p<0.05). Conclusion: Significant alterations in ECG and HRV in dystrophinopathies were showed compared to healthy children of similar age. Thus, electrical abnormalities may be the earliest manifestation of the histopathological process conducive to the development of cardiac dysfunction.