Dogs were anesthetized with sodium pentobarbital and ventilated with a respirator. Pressures were monitored in each chamber. Tissue samples from the beating heart were rapidly removed from uniform sites in the left ventricle (LV), right ventricle (RV), left atrium (LA), and right atrium (RA) and analyzed for ATP, ADP, and creatine phosphate (CP). The concentrations of ATP, ADP, and CP were distributed in the following order: LV > RV > LA > RA. This is the same order as the mean pressures developed in the various chambers, but the relationship between mean pressure and high-energy phosphate stores was not linear. The finding that ATP, ADP, and CP concentrations were highest in the LV, the chamber which performs the most work, suggests that differences in the distribution may be due to differences in the rates of production. © 1974, SAGE Publications. All rights reserved.