Anaerobic heat production by the heart.

Metabolic processes that release energy within the myocardium can be separated into aerobic metabolism, i.e., chemical reactions consuming O2, and anaerobic metabolism, defined here as chemical reactions not consuming 2, even though 02 may be present in the environment. The total energy that is set free by both types of process appears partially as heat within the myocardium and partially as mechanical work, which escapes from the heart, eventually to be dissipated as heat elsewhere in the body. For our purposes it will be convenient to express the energy transformation within the heart as follows: energy from aerobic metabolism + energy from anaerobic metabolism = external work + local heat. In this equation, energy arising from either aerobic or anaerobic metabolism may contribute to the mechanical work performed by the heart. In aerobic metabolism the amount of energy yielded per unit volume of °2 consumed varies only slightly with the type of substrate oxidized (1). Therefore, the rate of energy release from aerobic metabolism by the myocardium should bear a nearly constant relationship to its rate of 0° consumption. Furthermore, if conditions could be created experimentally where both anaerobic metabolism and external work were eliminated, heat production by the myocardium would bear a quantitative relationship to its 02 consumption. It should be possible to determine 02 consumption and heat production directly. Once their quantitative relationship was established at a time