Summary.We investigated whether L-arginine, used in heart preservation to limit endothelial damage, may influence the pool of amino acids during long term ischemia and reflow. Isolated isovolumic rat hearts (n 23) were submitted to 8h of hypothermic ischemia after cardioplegic arrest with the Centre de Rsonance Magntique Biologique et Mdicale (CRMBM) solution with or without L-arginine (Arg and No Arg groups respectively). Hearts were freeze-clamped after ischemia (n 11) or submitted to 60min of reflow (n 12) and freeze-clamped. Eight hearts were perfused aerobically for 20min and freeze-clamped (No ischemia group). Addition of L-arginine to the CRMBM solution limited aspartate depletion and decreased lysine level at the end of ischemia. After reflow, L-arginine supplementation increased the pool of glutamate and arginine and limited the depletion of serine, asparagine, glycine and taurine. We conclude that adding L-arginine to the CRMBM cardioplegic solution during long term ischemia preserved the amino acids pool.