In frogs, positive inotropic effects are transmitted catecholaminergically as they have been blocked with propranolol but not with atropine. Positive chronotropic effects were in some experiments blocked with atropine and not with propranolol (a "cholinergic type" of of positive chronotropic effect), the opposite occurred in other experiments (an "adrenergic type"). The cholinergic positive chronotropic effects were observed with the initial slow heart rate and were accompanied by negative inotropic effects; the chronotropic effect itself appeared suddenly (with no gradual acceleration of heart rate) and disappeared just as suddenly. The adrenergic effects, on the contrary, were observed with the initial rapid heart rate; they were accompanied by positive inotropic effects and developed and disappeared gradually.