For purpose of discussion, assume that the impulse propagates at the normal ventricular conduction velocity of 1 m/sec and that it takes 300 ms (0.3 sec), i.e. the normal refractory period of ventricular myocardium, for the fiber to repolarize to -60 mv, the transmembrane voltage at which the muscle regains it ability to be re-excited. The minimum distance an impulse must travel to return to the re-excitable tissue is determined by the product of its conduction velocity and its refractory period. In this situation, this is 1 m/sec x 0.3 sec which equals 0.3 m (30 cm) or approximately 12 inches.