The purpose of this study was to study the role of anisotropic distribution of conduction velocity in the initiation and perpetuation of ventricular tachycardia in an experimental model of sustained reentrant ventricular tachycardia in the Langendorff perfused rabbit heart. The hearts of 30 rabbits were used in the study. The right ventricle, the interventricular septum and the endocardial and intramural layers of the left ventricle were destroyed by freezing. In the surviving epicardial layer an obstacle was created using a cryoprobe. Thus, the final preparation consisted of a perfused ring of epicardium in the left ventricle. In 27 of 30 experiments programmed electrical stimulation induced sustained reentrant excitation around the obstacle. The cycle length of the tachycardia ranged from 128 to 197 ms in different experiments (mean 162 +/- 17 ms). During tachycardia in some segments of the ring the impulse propagated parallel to fiber orientation at a mean conduction velocity of 61 +/- 7 cm/s whereas in other segments of the ring the impulse propagated perpendicular to fiber orientation at a mean conduction velocity of 22 +/- 4 cm/s. An excitable gap was present during all episodes of tachycardia. In conclusion, conduction velocity during reentrant tachycardia depends on the relation between direction of propagation and fiber orientation. This anisotropic distribution of conduction velocity can play an important role in the initiation and perpetuation of ventricular tachycardia.