Cardiac energetics

The heart is a molecular machine that directly converts the chemical energy of ATP into heat and work. We detail the fundamental thermodynamics underpinning cardiac energy conversion, with interest placed on the efficiency of the conversion. We describe some of the numerous experimental techniques and cardiac preparations (in situ, in vitro, ex vivo, and in vivo) that allow the separation of cardiac energy expenditure into conceptually distinct components: basal metabolism, activation metabolism, force generation, myocyte shortening, and the resultant achievement of force-length work (at the level of the myocyte) and pressure-volume work (at the level of the whole organ). Our focus on experimental results related to physical exercise is supplemented by inclusion of thermodynamically-constrained mathematical simulations of the effects of exercise on the energetics of the heart. © 2019 Elsevier Inc. All rights reserved