This study was performed to assess the accuracy of 31P magnetic resonance spectroscopy (MRS) in the evaluation of myocardial ischemia in cats. Twelve cats underwent myocardial ischemia and reperfusion induced by 90 minutes ligation followed by 90 minutes recirculation of the left anterior descending coronary artery (LAD) MRS was performed using a 4.7T Biospec MRS/MRI system (Bruker, Switzerland). An inner diameter-1.5cm-sized doubly tuned surface coil was used for the collection of the MR signal. The coil was implanted to the epicardial surface at the expected area of infarction. 31P MRS was acquired before and during the periods of ischemia and reperfusion with 5-mimute to 30-minute of intervals. After completion of the 31P MRS study, animals were sacrificed and the hearts were excised for 2, 3, 5-triphenyl tetrazolium chloride (TTC) histochemical staining. The area of infarct was measured on the photographs of TTC stained heart slices using a computer programmed planimetry and the results were compared with those of the 31P MRS study. The level of phos- phocreatine (PCr) was decreased to 28.2$pm$6.9% of the baseline level 90minutes after occlusion and recovered phocreatine (PCr) was decreased to 28.2$pm$6.9% of the baseline level 90 minutes after occlusion and recovered to 43.8$pm$4.8% of the baseline level at the end of the reperfusion. A 50% depletion fo PCr was reached 5 minutes after the LAD occlusion. The ATP was decreased to a 26.6$pm$3.6% of the baseline level 90 minutes after occlusion and recovered to a 35.9$pm$6.0 of the baseline level 90 minutes after reperfusion. The decreasing rate of ATP was slower than that of PCr showing a 50% of depletion 15 minutes after occlusion. The PCr/ATP ratio was 1.16$pm$0.09 at the baseline, decreased to 0.88$pm$0.07 at 30 minutes of occlusion, and then progressively increased during the late ischemic and reperfused periods. The ratio of the infarcted area to the effective signal area of the surface coil was inversely correlated to the ATP (r= 0.68) and PCr (r=0.40) levels obtained at the end of reperfusion. In conclusion, 31P MRS reflects the changes in myocardial high energy phosphorous metabolism during the actue ischemia and reperfusion. If on adequate localization technique is feasible, 31P MRS can be used clinically in the diagnosis and monitoring of the patients with acute myocardial infarction