Objective: The aim of this study was to evaluate the safety and efficacy of the Cardi-O-Fix plug used for the treatment of muscular ventricular septal defects. Methods: We retrospectively reviewed the medical records of five patients with muscular ventricular septal defects who underwent transcatheter closure using the Cardi-O-Fix Plug, from November 2017 to August 2019. The median age was 5.1 years (range: 3.2–6.5). Their median body weight was 18.1 kg (range: 13.4–21.8). All the patients underwent detailed two-dimensional Doppler and colour flow imaging by transthoracic echocardiography. The left ventricular median defect size of the muscular ventricular septal defects was 5.6mm(range: 5.3–7.0). The right ventricular median defect size of the muscular ventricular septal defects was 3.9mm (range: 3.3–4.7). All the procedures were performed on beating hearts. Results: All the patients underwent successful device implantation with no displacement or detachment, they have complete echocardiographic closure at the 1-year follow-up. There were no occluder-related arrhythmia, chordae tendineae rupture, tricuspid insufficiency, aortic regurgitation, haemolysis, or embolisation. Conclusions: Application of the Cardi-O-Fix plug appears to be a feasible, safe, and effective treatment option for patients with muscular ventricular septal defects. Longer follow-up periods are warranted to prove the conclusion for long-term outcomes.