Comparison of the effects of chronic amiodarone on maximum rate of rise of action potential upstroke (Vmax) and conduction time between pulmonary vein (PV) (left, n = 6) and left ventricular (LV) wedge (right, n = 4) preparations. A: Action potentials (APs) recorded simultaneously from 2 sites of a PV sleeve preparation. B: APs recorded simultaneously from endocardial (Endo), epicardial (Epi), and midmyocardial (M) regions together with a pseudo-ECG in a LV wedge preparation. Lower panels show the rate dependence of Vmax normalized to the value at a basic cycle length (BCL) of 2,000 ms. Data are expressed as mean ± SD. *P < 0.05, chronic amiodarone versus control.