Inclusion Criteria:

• VSD must be diagnosed by acknowledged methods, like echocardiography
• Signs of left ventricular volume overload are present (left ventricle or left atrium diameters 2 standard deviations greater than normal) and/or measured by catheterisation : Qp/Qs > 1.5
• Pulmonary vascular resistance is less than 4 Wood units
• The patient is older than 24 months
• The VSD has a perimembranous or muscular location.
• A distance between the rim of the VSD and the aortic annulus of at least 3.0 mm (as measured on the 2-D echocardiography - apical 5-chamber view)
• The minimal diameter (size) of the VSD is less than 8.0 mm (as measured on the 2-D echocardiography - apical 5-chamber view)
• Patient must agree to fully participate in the clinical trial and give informed consent in writing. If the patient is without legal ability additionally the person of legal responsibility must agree and s/he must give the informed consent in writing

Exclusion Criteria:

Pathological or physical condition precluding the implantation of a Nit-Occlud® Lê VSD coil, such as :

• perimembranous VSD with no evidence of circular aneurysm formation
• Associated cardiac anomalies requiring surgery (greater than mild aortic insufficiency; such as aortic valve prolapse)
• Active endocarditis or other type of sepsis or other active infection at time of implantation
• Thrombus at or near the intended site of implantation
• Thrombus in the vessels through which access to the VSD is gained (unless the patient is protected with an embolic protection device such as a vena cava filter)
• Vessels through which access to the VSD is gained can not accommodate a 7 F sheath
• Potential steric (3-dimensional) interference of the occluder with intracardiac or intravascular structures (like valves)
• History of blood disorder (coagulopathy, tendency towards haemolysis)
• History of hypersensitivity to contrast medium or Nitinol
• AV-block II° or III°, atrial fibrillation, or atrial flutter
• End stage cardiac disease, irreversible major organ failure, or terminal cancer
• HIV infection
• Cerebrovascular disease or neurological deterioration
• Emergency cardiologic intervention
• Patient*) is not able to fully participate in this study including all follow-ups (e.g. for mental or geographical reasons, or patient is intravenous drug user or has strong potential for non-compliance to medical regimes)
• Patient, respectively the person of legal responsibility, is mentally unable to understand the nature, aims, or possible consequences of the clinical investigation
• Pregnant or breast-feeding women
• Patient did participate in another clinical investigation during the last 3 months
• Patient or the person of responsibility has revoked the consent.