When hearts are stressed by disease, energy substrates, called purines, wash out of the cell and the total pool of cellular energy becomes severely depleted. Disease also disrupts the heart's ability to recycle its remaining energy through the oxidative phosphorylation mechanisms. The combination of energy pool depletion and metabolic dysfunction contributes to the severity of the disease and impacts the physiological health of the heart. The same is true for skeletal muscles that are stressed through disease or high-intensity exercise.