Heart failure (HF) is the leading cause of death in PAH patients, but under current guidelines there is no treatment directed specifically at the failing right ventricle (RV). In a model of RV HF induced by PAH we examined whether a selective β1AR blocker (BB) metoprolol could slow adverse myocardial remodeling.A single injection of monocrotaline (60 mg/kg, MCT) in male Wistar rats was used to induce PAH leading to RV HF. Control (CON) animals were injected with saline. MCT animals were given metoprolol (10 mg/kg/day, BB group) or placebo (MCT group) daily by oral administration from 15 days post injection. Langendorff-perfused hearts were used for RV myocyte isolation (for functional experiments) or preparation of RV myocardial homogenates (for protein expression via Western blotting). Experiments were performed on the day MCT animals showed HF signs or on the median MCT HF day for BB/CON groups.In response to selective β1AR stimulation (isoproterenol 100nM with 100nM ICI118,551) MCT RV myocytes had a blunted increase in fractional shortening and rate of relaxation compared with CON (P