Myocardial ischemic arrest, using a cold crystalloid cardioplegic solution, decreases intracellular concentrations of glutamate (from 6.2 +/- 0.5 to 4.5 +/- 0.45 micromol/g wet weight, n = 19, P < 0.05) and ATP (from 3.0 +/- 0.4 to 1.9 +/- 0.3 micromol/g wet weight, n = 9, P < 0.05) but not aspartate. After 20 min of normothermic reperfusion, the fall in glutamate and ATP was maintained (4.5 +/- 0.52 and 2.0 +/- 0.2 micromol/g wet weight, respectively), and there was a fall in aspartate (from 1.32 +/- 0.12 to 0.9 +/- 0.1 micromol/g wet weight). Myocardial arrest with cold blood cardioplegic solution did not cause a significant fall in tissue ATP, glutamate, or aspartate. However, after reperfusion all three fell significantly. With the exception of a fall in tissue valine during ischemia with cold crystalloid cardioplegic solution and a rise in alanine during ischemia with cold blood cardioplegic solution, there were no significant changes in tissue alanine, valine, leucine, or isoleucine during ischemia or after reperfusion using crystalloid or blood cardioplegic solutions. This work documents the changes in the intracellular concentrations of important metabolites in the hearts of patients undergoing coronary artery surgery using different myocardial protection techniques.