[en] Myocardial metabolism was studied in 6 closed chest dogs with ³¹P NMR (using a cardiac window model and an external surface coil) before, during and after production of acute hypertension with catecholamines. As heart work (defined as heart rate X mean arterial blood pressure product, HR x MABP) was increased, inorganic phosphate/phosphocreatine (Pi/PCr) ratio increased. The Pi/PCr vs. workload relationship is an indicator of the rate of oxidative-phosphorylation. These data indicate that under conditions of acute hypertension, heart muscle responds to increased work loads in a manner similar to skeletal muscle. The possibility of obtaining this type of data from an intact closed chest animal has implications for use of this technique to evaluate clinical heart disease