The corticotropin-releasing factor (CRF) system has been shown to exert physiological actions in the cardiovascular system of mammals, including positive inotropy and cardioprotection against ischemia-reperfusion injury. In contrast, little is known about the cardiac CRF system in non-mammalian species. I investigated the role of CRF in the cardiac response to acute hypoxia in rainbow trout. I examined myocardial contractility during hypoxia/reoxygenation by measuring ventricular pressure generation of ex vivo Langendorff-perfused hearts and investigated the effects of pre-treatment with 1.0 nM trout CRF or 10 nM antalarmin, a CRF type 1 receptor antagonist. All CRF system components are expressed in the heart where the dominant receptor type is CRF-2b and the dominant ligand is CRFa1. Antalarmin exerted significant negative inotropic and lusitropic effects throughout the hypoxia exposure and recovery periods. These results suggest that endogenous CRF plays a cardioprotective role during hypoxia/reoxygenation and is involved in the maintenance/recovery of cardiac function.