Aminophylline was selectively perfused through either the sinus node or through the AV (atrioventricular) junction of 35 intact canine hearts in situ. The positive chronotropic action observed was equally powerful in accelerating either sinus rhythm (50 ± 8% increment) or AV junctional rhythm (55 ± 10% increment). This positive chronotropic effect has at least three distinct components: a major direct action on autonomic centers, a lesser effect due to local catecholamine release, and a part due to peripheral vagolytic action.
