Catecholaminergic stimulation is sufficient to cause T-wave inversion. (A) In awake and undisturbed pythons (n = 8), the intra-arterial administration of adrenaline (5 µg kg⁻¹) had no effect on the R amplitude, but caused inversion of the T-wave in seven animals. (B) In awake and undisturbed pythons (n = 8), the intra-arterial administration of isoproterenol 5 µg kg⁻¹, a β-adrenergic agonist, had no effect on the R amplitude, but caused a substantial shortening of the time to repolarization and an inversion of the T-wave in all animals.