Prenatal protein restriction in utero predisposes offspring to hypertension in adulthood. β-adrenergic receptor blockade is one standard therapy for the treatment of hypertension, however, gender related differences in responsiveness to β-blocker exist. Hypertensive women receiving β-antagonists exhibit significantly higher rates of treatment failure than men. This study compares the effectiveness of β-blocker therapy in adult female rat offspring from control and protein restricted dams in attenuating the isolated hearts response to β-adrenergic receptor stimulation. Pregnant Wistar rats were fed either a control (CON, 180g casein/kg n=10) or a low protein (MLP, 90g/kg n=10) diet throughout gestation. At birth, mothers were fed laboratory chow and the offspring weaned onto the same diet at 4 weeks of age. At 6 months, rats fed either diet were treated with the β1-blocker Metoprolol (+BB (n=5)), administered via drinking water for 2 weeks (100mg/Kg a day). Controls received water only (-BB (n=5)). At cull, hearts were rapidly excised and cannulated via the aorta to Langendorff apparatus. Hearts were retro-perfused with Krebs-Henseleit buffer bubbled with O2/CO2 and maintained at constant pressure (60 mmHg) and temperature (37°C). Left ventricular pressure function (LVP) and heart rate (HR) was monitored by insertion of a pre-calibrated pressure transducer and latex balloon. Following a period of equilibrium, each heart received 100μl of increasing doses of Isoproterenol (0-72μM) where contractile function recovered to baseline between doses. Sigmoidal dose response curves were produced using non linear regression, and t tests determined whether the effects of β-blocker on logEC50 and Hill slope values were altered by maternal dietary groups. Isolated hearts from CON+BB and CON-BB had similar chronotropic responses to β-agonist treatment. In contrast, Metoprolol treatment significantly increased the MLP isolated hearts response to the non-specific β-agonist Isoproteronol. (P<0.0001 for both max LVP and AUC LVP). Similar findings were evident when investigating the chronotropic responses of the isolated female heart to β1-blocker therapy. Maximal HR and AUC for HR in CON fed rats treated with Metoprolol showed no difference in sensitivity to β-adrenergic receptor stimulation. However, hearts from MLP offspring had an increased response to Isoproterenol following β-antagonist treatment, logEC50 and Hill slope of curves for maximal HR and AUC for HR were significantly higher at the P<0.001 and P<0.005 level respectively. In conclusion this study establishes that ex vivo hearts from programmed hypertensive offspring exhibit increased sensitivity to β-agonist stimulation following treatment with the β1-antagonist Metoprolol. Further work is required to determine whether the same negative effects are seen in vivo.