Ventricular septal defect (VSD) is most common congenital heart disease (15-20%) [Hoffman, 2002] and about 70% of these are perimembranous (PmVSD). The traditional treatment, if necessary, is surgical repair - VSD closure using the autologous pericardium or synthetic material such as polytetrafluorethylene (PTFE). There are two types that are commonly in use - GORE TEX Cardiovascular patch (GRTX) and BARD Edwards Outflow Tract Fabric knitted PTFE (BARD). Polytetrafluorethylene (PTFE) polymers are successfully used to repair as large diameter VSD and small VSD as well. For surgical operation there are usually used synthetic patch, uninterrupted (continuous) and interrupted suture technique, and transatrial access with cardiopulmonary bypass, cardioplegia in aortic root and local myocardial hypothermia Most patients undergo the operation in the first year of life6, therefore the structure of the myocardial tissues is more soft in contrast with age two or more years old child tissues characteristics, concerning the used material for VSD closure. At the moment of exposure of VSD, considering localization, size and shape of the VSD, we make a decision, which material is more suitable in certain case. We suspect that knitted material (BARD) would be more appropriate to be with greater accordance to myocardial tissues and it has the advantage of making less myocardial and conduction tissue trauma and being more fitted for good shaping of VSD patch to avoid residual defects. [Stark, 1986]. The goal of this research was to investigate the biomechanical properties of two synthetic materials, such as the PTFE material patches - GRTX and BARD in vitro, and compare the main biomechanical parameter of these materials.