Ischemia is the most common and important cause of injury to cardiomyocytes. Acute ischemia causes profoundderangement of the cellular energetics and metabolism, and this ultimately leads to cell death. Experimentalstudies have demonstrated the presence of an endogenous protective mechanism that can diminish or delay celldeath from ischemic insult; this is known as ischemic preconditioning. In this review, we summarize the recentknowledge of the cellular biology of acute ischemic injury and also signaling mechanisms of cardioprotectionthat are involved in preconditioning. Further, we briefly discuss the clinical implications. (Korean Circulation J2006;36:165-177)