We compared the effects of cicletanine (10 mg/kg i.v.) and verapamil (0.1 mg/kg i.v.) on heart rate, ventricular effective refractory period, systolic and diastolic arterial blood pressure and overpacing-induced ST-segment elevation detected by right ventricular intracavital electrogram in conscious rabbits. Cicletanine significantly reduced overpacing-induced ST-segment elevation, which is an indicator of myocardial ischemia, and heart rate, but did not influence blood pressure and ventricular effective refractory period. Verapamil did not significantly influence ventricular effective refractory period, blood pressure or heart rate, but reduced the ST-segment elevation induced by frequency loading. These results suggest that acute treatment with cicletanine induces an anti-ischemic effect in the overpaced heart of conscious rabbits.