Although this chapter is devoted to a discussion of myocardial metabolism, it should be understood that all energy-requiring processes in the biosphere are dependent on capture of solar energy and its entrapment in molecules that can be used to fuel biological processes such as cardiac contraction. The synthesis by plants of molecules such as glucose from CO2 and H2O is powered by the sun via the process of photosynthesis. Photons radiated by the sun are trapped by chlorophyll and used to drive the synthesis of adenosine triphosphate (ATP). ATP has two phosphate bonds with high levels of stored chemical energy (Fig. 1).