A constant supply of oxygen is indispensable for cardiac viability and function. However, the role of oxygen and oxygen-associated processes in the heart is complex, and they and can be either beneficial or contribute to cardiac dysfunction and death. As oxygen is a major determinant of cardiac gene expression, and a critical participant in the formation of ROS and numerous other cellular processes, consideration of its role in the heart is essential in understanding the pathogenesis of cardiac dysfunction.

The mammalian heart is an obligate aerobic organ. At a resting pulse rate, the heart consumes approximately 8–15 ml O 2/min/100 g tissue. This is significantly more than that consumed by the brain (approximately 3 ml O 2/min/100 g tissue) and can increase to more than 70 ml O 2/min/100 g myocardial tissue during vigorous exercise (1, 2). Mammalian heart muscle cannot produce enough energy under anaerobic conditions to maintain essential cellular processes; thus, a constant supply of oxygen is indispensable to sustain cardiac function and viability. The story of oxygen in the heart is complex, however, and goes well beyond its role in energy metabolism.