Myocardial lipid and lactate levels are sensitive indicators of biochemical status: lipid levels have been shown to increase in response to high fat diets, disease or metabolic stress and elevated lactate levels are indicative of reduced oxygen supply. Selective measurement of lactate or lipid levels by 1H NMR is not straightforward since both the lactate methyl group and lipid methylene groups resonate at 1.3 ppm. We have overcome this difficulty by employing spectral editing techniques to observe both lipid methylene and lactate methyl resonances, and have measured lipid and lactate levels in perfused rat hearts during control perfusion and in response to metabolic stress. Lactate increased during ischemia and decreased during reperfusion, and the ischemia-induced increase is inhibited by iodoacetate, as expected. In contrast, lipid levels increased during ischemia and remained elevated during reperfusion. Hearts from rats fed high fat diet show elevated lipid levels during control perfusion. Data obtained by 1H NMR are consistent with biochemical data, validating the technique.