This article is a short review of newer findings concerning the physiological and biochemical bases of the heart's tolerance to ischemia. The following themes are discussed. I. Energy-pool, energy-demand, and efficiency of anaerobic metabolism, the essential determinants of reanimation time and the heart's tolerance to ischemia. II. Experimental results of ischemic heart arrest and the heart arrest induced by a sodium-poor calcium-free, procaine-containing cardioplegic solution, developed by the author. III. Equivalents of function, metabolism and structure during the anaerobic period of the myocardium. IV. The myocardium's capability to recover in dependence on the metabolic state of ischemia and summary of the most important points of gaining a long time of tolerated ischemia. V. Survey and prospects.