In isolated rat hearts effects of chloropyramine (CP), histamine H1 antagonist, and famotidine (FA), H2 antagonist, upon two different myocardial injuries, ischaemia-reperfusion and hypoxia-reoxygenation were studied. In both types of injury the effects of drugs were seen mainly during reperfusion and reoxygenation, respectively. During reperfusion neither CP nor FA influenced amplitude of contractions, but CP lowered heart rate, +dp/dtmax and coronary flow. During reoxygenation CP and FA lowered early posthypoxic contractions, whereas CP decreased and FA increased heart rate. CP and FA did not significantly influence the post-ischaemic and posthypoxic lactate dehydrogenase (LDH) release. Present results indicate the existence of H1 and H2 receptors in rat heart as well as their involvement in both types of studied injuries.