β-Adrenergic receptor blockade prevents T-wave inversion during heating. (A) The bar graph shows changes in HR upon first propranolol (5 mg kg⁻¹) administration, then heating to 36°C, and finally isoproterenol (5 µg kg⁻¹) administration. HR increased significantly during heating (ANOVA [repeated measurements], P = 0.0013). (B) Example of lead I (upper) and lead aVF (lower) before and after heating in the presence of propranolol. (C) Example of vector cardiogram before and after heating in the presence of propranolol. (D) Bar graph showing the amplitude of the T-wave in lead I and aVF before (blue dots) and after (red dots) heating. T-wave amplitude did not change upon heating in lead I and aVF (paired t test; P = 0.43 and P = 0.56, respectively). (E) Python 16 exhibited ventricular premature beats (VPBs), which was preceded by T-wave alternans (examples are indicated with red arrowheads).