Abstract: In order to further study the changes of dehydrogenases in acute myocardial ischemia (AMI), the present experiments were performed in a rabbit model of ligating left anterior descending coronary artery for 0.25, 0.5, 1, 1.5, 2, 4, 6, 12, 24, 36 and 72 hours. Tde rusults showed: (1) By 6 hours of AMI, the activity of seminal lactate dehydrogenase (LDH) was obviously high, its difference between pre-ischemia and post-ischemia was 734±153.66nmol/L (Mean±SE, P<0.05, t test). (2) At 0.5 hours after coronary ligation, the myocardial infarction was identified by macroscopic histochemistry. (3) At 1 hour after coronary ligation, LDH and malate dehydrogenase (MDH) depleted, so did succinate dehydrogenase(SDH) at 2 hours after ligation By microscopic histochemistry. LDH and MDH were more sensitive than SDH in AMI. (4) The changes of local enzymatic histochemistry of ischemic myocardium occured prior to the total serumal enzymatic ones.