Higenamine caused the postive chronotropic effect. This response became prominent as the ca²⁺ concentration in the bathing solution lowered. When tetrodotoxin was added to the bathing solution, the effect of higenemine altered and became similar to that of epinephrine. Higenamine reduced the relative threshold voltage of the right atrium in the bathing solution with [ca²⁺] of 0.5mM. Such effect was abolished by tetrodotoxin. The effects of verapamill on the spontaneous rate and the relativel threshold voltage were inhibited by higenemine. The above results suggest that, aithough the main action og higenamine is on the Ca channel, higenamine also have a minor effect of augmenting the Na channel.