In vivo left ventricular pressure recordings. (A) Baseline +dP/dtMAX (mmHg/s). (B) +dP/dtMAX (mmHg/s) 2 min after isoproterenol administration (10 μg/kg, i.p.). (C) Percentage increase in +dP/dtMAX from baseline to isoproterenol condition. (D) Baseline −dP/dtMAX (mmHg/s). (E) −dP/dtMAX (mmHg/s) 2 min after isoproterenol administration (10 μg/kg, i.p.). (F) Percentage decrease in −dP/dtMAX from baseline to isoproterenol condition. (G) Baseline heart rate (HR) (bpm) measured by pressure waveform. (H) HR 2 min after isoproterenol administration (10 μg/kg, i.p.). (I) Percentage increase in HR from baseline to isoproterenol condition. All error bars represent SEM. Sample size (n) is indicated for each group in parentheses. *P < 0.05, ***P < 0.001, Student’s t-test.