In order to determine if an increase in myocardial oxygen consumption is accompanied by changes in high energy phosphates in normal subjects and patients with dilated cardio‐myopathy, phosphorus‐31 spectra were acquired under resting conditions and during do‐butamine infusion. In seven normal subjects, dobutamine raised the rate‐pressure product to 226% of control. The ratio of PCr/ATP was 1.86 ± 0.17 (mean ± SE) under resting conditions and 1.90 ± 0.22 (P = 0.44) with dobutamine infusion. In eight patients with dilated cardiomyopathy, dobutamine raised the rate‐pressure product to 161% of control. As in the normal subjects, the ratio of PCr/ATP under resting conditions (1.63 ± 0.24) was unchanged during dobutamine infusion (1.57 ± 0.24, P = 0.38). These data indicate that increases in cardiac work do not have a major effect on high energy phosphate concentrations in normal subjects or in patients with clinically compensated dilated cardiomyopathy. © 1992 Academic Press, Inc.