The purpose of this study was to investigate, in an anesthetized pig model of low-flow myocardial ischemia, the electrophysiologic effects of the class III drug d-sotalol during myocardial ischemia. Serial monophasic action potential (MAPD90) recordings and refractory period determinations from the anterior and posterior left ventricular wall were taken in 25 pigs during baseline, after low-flow posterior wall ischemia, after d-sotalol infusion under nonischemic conditions, and after repeated posterior wall ischemia while continuing the drug. Measurements were done at 60 and 150 beats/min after radiofrequency ablation of atrioventricular conduction. At baseline, MAPD90 and refractory periods were comparable in the anterior and posterior wall (323 +/- 15 vs. 318 +/- 10 ms, and 267 +/- 10 vs. 262 +/- 11 ms at 60 beats/min, respectively). In the absence of d-sotalol, low-flow regional ischemia was associated with a significant shortening of MAPD90 in the posterior versus the anterior wall (267 +/- 20 vs. 317 +/- 20 ms at 60 beats/min; p = 0.006). Similarly, ischemia-induced shortening of the refractory periods in the posterior wall was apparent (230 +/- 16 ms in the posterior wall vs. 274 +/- 14 ms in the anterior wall at 60 beats/min). In contrast, ischemia was no longer associated with shortening of MAPD90 (360 +/- 17 ms posterior wall and 360 +/- 20 ms anterior wall at 60 beats/min) and refractory periods (304 +/- 19 ms posterior wall vs. 316 +/- 15 ms anterior wall at 60 beats/min) during combined posterior wall ischemia and d-sotalol infusion. Similar findings were obtained during pacing at 150 beats/min. d-Sotalol attenuates ischemia-induced action potential shortening. This property should decrease dispersion of cardiac repolarization and be antiarrhythmic. On the other hand, longer APD under ischemic conditions may favor calcium overload, which may trigger new arrhythmias.