BACKGROUND Preserved energy metabolism is essential for myocardial viability and the creatine kinase reaction is central to energy production and reserve. Although the appearance of myocardial creatine kinase enzyme in the blood is widely used to diagnose cardiac necrosis, there are no non-invasive ways to measure local creatine concentrations in the healthy and diseased human heart. METHODS We measured total myocardial creatine by spatially-localised, water-suppressed hydrogen magnetic-resonance spectroscopy (1H-MRS) on a clinical (1.5 T) magnetic-resonance-imaging system in ten healthy volunteers (controls) and ten patients with a history of myocardial infarction. We validated this technique by comparison of 1H-MRS values of creatine with biopsy assays in an animal model of infarction. RESULTS Total creatine was measured in the posterior and anterior left ventricle and septum, and was significantly lower in regions of infarction (10 [9] SD micromol/g wet weight) than in non-infarcted regions (26 [11] micromol/g, p=0.001) of myocardium in patients or in the myocardium of healthy controls (28 [6] micromol/g, p<0.0001). CONCLUSIONS Spatially localised 1H-MRS can be used to measure total creatine non-invasively throughout the human heart. The detection of regional creatine depletion may provide a metabolic means to distinguish healthy from infarcted non-viable myocardium.