The 5-HT-2 antagonist ketanserin (KAS) has been successfully used to treat acute hypertension in coronary bypass surgery. The present study was performed to investigate the effect of KAS on ischaemic myocardium. In 11 anaesthetized (piritramide) dogs, systolic contraction (sdL) and end-diastolic length (edL) of myocardium supplied by the left descending coronary artery (LAD) and the left circumflex coronary artery (LCX) were measured by sonomicrometry simultaneously with aortic pressure (AoP), left ventricular dP/dtmax and end-diastolic pressure (LVedP), heart rate (HR), stroke volume, and LAD flow (QLAD). Regional ischaemia to decrease sdLLAD (-48%) was achieved by LAD stenosis (QLAD -47%). Concomitantly, edLLAD increased by 8%. However, the other variables did not change. Then KAS was given i.v. (0.15 + 0.15 + 0.30 + 0.6 mg/kg) at 15-min intervals. Following KAS, prestenotic sdLLAD recovered in a dose-dependent manner. LVedP and edLLAD decreased, sdLLCX increased, and the other variables were not affected. This functional recovery of ischaemic myocardium was attenuated by pretreatment with metoprolol (MET, 1 mg/kg) prior to LAD stenosis. The ischaemic area was not irreversibly damaged, however, as proven by the recovery of prestenotic sdLLAD values after release of the stenosis. The improved systolic shortening of ischaemic myocardium following KAS did not result from restored QLAD due to post-stenotic vasodilation or break up of platelet aggregates (QLAD did not increase) or from reduced afterload (AoP did not decrease). Obviously, it was mediated by beta-1-receptors, as shown by the attenuation of the beneficial effect of KAS by pretreatment with MET.