The subepicardial: subsendocardial ratio of Rb 86 contents was measured and used as an index of the distribution of coronary blood flow to the more superficial and deeper layers of the canine myocardium. In the normally beating heart, the level of intraventricular pressure did not exert any detectable influence upon this ratio of Rb 86 contents. In the fibrillating heart, or in an ischemic (and presumably non-beating) region of the beating heart, on the other hand, this ratio increased as intraventricular pressure was progressively raised. It is concluded, therefore, that the intraventricular pressure exerts a significant influence upon the distribution of blood flow to the deeper and more superficial layers of myocardium only in regions which are not beating normally.

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