Abstract: The protective effects of m -Nif 15, 30 and 50μg·kg^-1 and of Nif30μg. kg^-1 on experimental myocardial infarction and metabolism in rabbits were evalu-ated. Blood samples were collected simultaneously from the femoral artery and thecoronary sinus for examining lactate and potassium balance. In the normal group (n = 8)and the sham ligated group (n= 5), the lactate balance were + 17±1.0 and + 13±1.1%respectively and the potassium balance were+ 2.1 ±0.08 and + 2.4±0.08%, respectively.After occlusion of the LAD, the lactate and K+ balance reduced to - 196±60. 2 and- 83.0±8.2% respectively, and m -Nifproduced a dose dependent improvement of bothbalance. After giving m- Nif 15, 30 and 50 μg ·kg^-1 iv, the lactate balance improved to-60±9, -48±6. 7 and -24±. 1.8% and the K⁺ balance went up to -32. 2±2. 1,-17.6 ±0.1, - 3.3 ±0.06, respectively. In the mean time, Nif 30μg·kg^-1 iv improved thelactate and K⁺ balances to -52±8.6% and -36. 4±3. 1%. In another experiment,propranolol 1 mg ·kg^-1 iv improved the lactate balance to -18±1.2% while theK⁺ balace increased to + 2.0±0.05%. The area of the myocardial infarct was measured by nitroblue tetrazolium (N- BT)technique 24 h after LAD occlusion, m - Nif 15, 30 and 50μg·kg^-1 caused significant reduc-tion of the infarct area by 12.6±1.1, 8.4±0.4and 5.6±0.3%. while Nif 30μg·kg^-1caused 9.2±0.9%, reduction, and propranolol 3.2±0.5%, in occlusion group 18.7±3.3%, solvent control 19±4. 0%. These results indicate that different doses of m-Nifsignificantly improved ischemic myocardium, m- Nif seems to have more beneficial effectsthan Nif in treatment of angina pectoris.