The goal of this chapter is to provide a review of the physiology and pathophysiology of myocardial ischemia. In the past, it was thought that a lack of blood flow to the heart resulted in irreversible myocardial damage and necrosis (infarction). However, more recent evidence has suggested that there are several clinical scenarios, in presentation falling between the basic definitions of ischemia and infarction, in which the heart may recover a variable degree of preischemic function even though some degree of necrosis has occurred. Furthermore, with technological advances that allow intentional cardiac arrest during cardiac surgery, as well as noninvasive cardiac angioplasty (opening) of occluded coronary arteries, the phenomenon of reperfusion injury has at the same time been added as a sometimes-debilitating clinical syndrome. This chapter explores these new ischemic syndromes and describes up-to-date means for protecting the heart from these conditions (cardioprotection).