BACKGROUND AND OBJECTIVES: The effects of artificial obstacles on the dynamics of ventricular fibrillation have been extensively investigated with an electrical mapping system. This study was performed to assess the influence of transmural obstacles on the dynamics of wavefronts, and determine whether these can convert ventricular fibrillation to ventricular tachycardia by stabilizing the wavefronts in the fibrillating right ventricular tissues of pigs, using an optical mapping system. MATERIALS AND METHODS: The right ventricles of pigs (n=15) were excised and placed in a tissue perfusion system, with the epicardium facing up. Holes, with increasing sizes, from 2 to 8 mm in diameter, were created using a skin biopsy punch. Another 8 mm sized hole was then made adjacent to the first, and the changes in the wavefront dynamics and cycle length of the optical action potential waves investigated. RESULTS: In 14 of the 20 obstacles, in ten tissues, transient attachment of electrical activities along the rim of obstacles and transient rotation of the wavefronts were observed. During baseline ventricular fibrillation, the fibrillation cycle length was 118.5+/-24.7 msec, which was increased to 135.4+/-30.2 msec after creation of the first hole, and to 159.4+/-47.7 msec after the second (p=0.01). There was a positive correlation between the obstacle size and cycle length (r=0.43, p=0.007). In three tissues, conversion to ventricular tachycardia from ventricular fibrillation was observed after creation of the two holes. CONCLUSION: Obstacles of an appropriate size had anti-fibrillatory effects in tissues with ventricular fibrillation, which was partly explained by the temporary attachment of wavefronts to the obstacles.