Background: The effects of artificial obstacles on the dynamics of ventricular fibrillation have been extensively investigated. However, most studies were performed with simulated tissues or using an electrical mapping system. This study was performed to assess the influence of the transmural obstacles on the dynamics of wavefronts and to determine whether obstacles can convert ventricular fibrillation to ventricular tachycardia by stabilizing wavefronts in fibrillating right ventricular tissues of pigs using an optical mapping system. METHODS: The right ventricles of pigs(n=15) were excised and placed in a tissue perfusion system with the epicardium facing up. The tissue was stained with di-4-ANEPPS. Quasimonochromatic light was shone on the tissues, and the fluorescence was collec- ted with charge-coupled device camera. A hole was created using a skin biopsy punch from 2mm to 8mm in diameter. Then, the other 8mm sized hole was made just beside the first hole. The changes of wavefront dynamics and the cycle length of optical action potential waves were investigated. RESULTS: In ten tissues, optimal signals were obtained and ventricular fibrillation was maintained. Transient attachment of electrical activities along the rim of obstacles and transient rotation of wavefronts were observed in 14 obstacles. These changes were found only in obstacles of 6 to 8mm. During baseline ventricular fibrillation, fibrillation cycle length was 118.5짹24.7 msec and this was increased to 135.4짹30.2 msec after 8mm hole, and to 159.4짹47.7 msec after 2 holes(p=0.01). There was a positive correlation between the obstacle size and cycle length(r=0.38, p=0.007). In three tissues, conversion to ventricular tachycardia from ventricular fibrillation was observed after creation of two holes. CONCLUSIONS: In conclusion, obstacles of proper size has anti-fibrillatory effects in tissues with ventricular fibrillation and this phenomenon was partly explained by the temporary attachment of wavefronts to the obstacles.