Abstract: The experiments were performed on 64 guinea pigs. Artificial respiration was carried out under general anesthesia. Before and after graded hypoxia lead Ⅱ electrocardiogram was recorded and myocardial adenosine level, blood K⁺, pH and po₂ Were measured to explore the relationship between dromotropic and chronotropic arrhythmias and endogenous adenosine during hypoxia by synchronous quantitative study of three variables-degree of poxemia, changes in electrocardiogram and myocardial level of adenosine. Experimental results disclosed that (1) A close relation existed between the changes in cardiac rhythm and endogenous myocardial adenosine caused by hypoxia; (2) aminophylliue antagonized the negative dromotropic and chronotripic arrhythmias and there existed a cause and effect relation between the endogenous myocardial adenosine and such hypoxia arrhythmias; (3) Vagal drive, K⁺ and pH had little if any bearing on the functional inhibition of the S-A and A-V nodes during the period of short-term hypoxia encountered in such cases.

Key words: adenosine, sinus bradycardia, A-V blook, myocardial hyPoxia