tokens: Both isomers of propranolol were capable of preventing adrenaline - induced cardiac arrhythmias in cats anaesthetized with halothane , but the mean dose of ( - ) - propranolol was 0 . 09 + / - 0 . 02 mg / kg whereas that of ( + ) - propranolol was 4 . 2 + / - 1 . 2 mg / kg .