[Mechanisms of "warm" tachycardia and "cold" bradycardia in cats].

The infusion of a small volume of blood with temperature higher ("warm") or below ("cold") the temperature of atrial blood into the right atrium induced "warm" tachycardia and "cold" bradycardia, resp., in anesthetized and in alert cats. Infusion of the blood with temperature equal to that of atrial blood induced no changes of the heart rate. Infusion of the same volume of "cold" or "warm" blood after adreno- and cholinoreceptor-blocking agents was accompanied by a less severe tachycardia or bradycardia. There seem to be two mechanisms in the initiation of the above effects: the neural and the myogenic ones.