The phospholipid composition of the crude plasma membrane fraction of Langendorff perfused rat hearts has been studied. The effect of phosphocreatine (PCr) and 3-phosphono-2-imino-1-methyl-4-oxoimidazolidine (PIMOI) on lysophosphoglycerides (LPG) level in this fraction isolated from hearts that were totally ischemic for 8 minutes, has been examined. The absolute and relative contents of LPG were significantly increased in ischemic hearts: the lysophosphatidylcholine content was elevated by 94% and that of lysophosphatidylethanolamine--by 77%. Accumulation of these LPG in ischemic myocardium was completely inhibited in the presence of 10 mM PCr or PIMOI in the perfusate. LPG may play a key role in the destruction of sarcolemma. Therefore, these data allow to assume that the protective effect of PCr and PIMOI on the sarcolemma of ischemic myocardium may be the result of their influence on the phospholipid metabolism in the ischemic region of the heart.