Abstract: In anesthetized rabbits arrhythmia (mainly ectopic beats) and striking elevation of arterial blood pressure could be elicited during and after stimulation of mamillary nucleus of the hypothalamus and its surrounding regions by monophasic square wave trains lasted 5-10 seconds (pulse duration: 0.5--1ms; frequency: 40-70 Hz; current intensity: 4-90μA). Stimulation of hypothalamus on rabbits by temporary occlusion of the carotid artery or neurectomy of the carotid sinus could elicit an increased response of arrhythmia.