The diversity of conditions inducing an increase in CPK-MB, CPK, LDH and SGOT allows investigation of the quantitative evolution in cardiac patients during heart surgery. In nine patients submitted to valve replacement, three samples were taken respectively: one from the superior and the inferior caval veins and one another from the coronary sinus and immediately centrifuged. The sera were processed to quantitate the CPK, CPK-MB, LDH and SGOT through the three periods of observation. The three sites intended to explore the possible other sources of CPK-MB released at surgery: superior vena cava accounts for upper body regions, inferior vena cava for lower body regions and the coronary sinus for the heart itself. The three sites compared separately through the three periods did not show any significant differences. Only comparing the pre-CPK values to their homologous obtained during and after cardiopulmonary bypass, very evident differences could be registered (P less than 0,05 and less) for CPK, CPK-MB and LDH. While SGOT remained totally unchanged through the three periods. The evolutive CPK, CPK-MB and LDH increase accounted for high sensitivity of these enzymes to the variations of conditions during cardiac surgery. It is highly possible that other sources of CPK-MB could be dissiminated in the body and capable to produce valuable enzymatic amounts during and after cardiac surgery and that the heart is not exclusively alone in releasing this enzyme during cardiac ischemic arrest and in other circumstances. The real importance of CPK-MB principally and of CPK would be surestimated as conclusive parameters in diagnosis of myocardial damages during cardiac procedures.(ABSTRACT TRUNCATED AT 250 WORDS)