Ligation of the coronary artery to produce myocardial infarction experimentally was performed in 41 mongrel dogs. The dogs were then treated with niludipine or nifedipine. Niludipine in doses of 0.05 mg/kg/day (niludipine A group) and 0.1 mg/kg/day (niludipine B group) or nifedipine 0.05 mg/kg/day (nifedipine group) was administered for 7 postoperative days. The animals were sacrificed, their hearts removed and extent of myocardial damage studied. 1. The size of infarctions measured by 99mTc-PYP myocardial scintigrams of the isolated heart was significantly smaller in the niludipine A group. 2. The degree of ischemia indicated by LDH isoenzyme patterns was lowest in the niludipine A group followed by nifedipine and niludipine B group in this order. The value for H subunits of LDH isoenzymes on the subepicardial side was higher in the nifedipine group. 3. Histopathological findings varied from specimen to specimen, but in general the niludipine A group showed best improvement. Our results suggest that the calcium antagonistic drugs, niludipine and nifedipine, seem to have myocardium protective properties in dogs. To what degree these findings can be applied clinically needs further studies.