The objective is to investigate the safety of the AMPLATZER Muscular VSD Occluder for the treatment of muscular ventricular septal defects, which are hemodynamically significant and are either isolated or in conjunction with other congenital heart defects in infants and children.

The objective of this feasibility study is to investigate the safety of the AMPLATZER Muscular VSD Occluder for the treatment of muscular ventricular septal defects, which are hemodynamically significant and are either isolated or in conjunction with other congenital heart defects in infants and children.

Inclusion Criteria:

• Patients with hemodynamically significant muscular VSD's (demonstrated by echocardiography or angiography), either isolated or in conjunction with other congenital heart defects
• Age < 18 years old

Exclusion Criteria:

• Less than 4 mm distance from the semilunar (aortic and pulmonary) and atrioventricular valves (mitral and tricuspid)
• Patients with severely increased pulmonary vascular resistance above 7 woods units and a right-to-left shunt and documented irreversible pulmonary vascular disease
• Patients with perimembranous (close to the aortic valve) VSD
• Patients < 3 kg
• Patients with sepsis (local/generalized)
• Patients with gastritis, gastric ulcer, duodenal ulcer, bleeding disorders etc. and other contraindications to aspirin therapy unless other anti-platelet agents can be administered for 6 months
• Inability to obtain informed consent