Isolated perfused heart preparations from guinea-pigs developed arrhythmic contractions following the administration of Ro 363 in doses producing 70-100% of its maximal chronotropic responses [1]. In spontaneously contracted tracheal preparations from the guinea-pig, RO 363 is a full agonist and is approximately half as potent as (-)-Isoprenaline. These effects of RO 363 are due to the activation of a population of β1-receptors in the tissue since RO 363 and (-)-Isoprenaline have the same relative potencies in trachea, cardiac and ileal preparations [2].

In chloralose-anaesthetized cats, Ro 363, when compared to epinephrine (adrenaline), is essentially devoid of arrhythmogenic activity in animals in which cardiac sensitization is induced by U-0882 or halothane [1].