Proton‐decoupled phosphorus‐31 heart spectros‐copy was performed in healthy subjects (n = 9) and patients with dilated cardiomyopathy (DCM, n = 9) or hypertrophic cardiomyopathy (HCM, n = 8). The phosphocreatine (PCr)‐to–adenosine triphosphate ratio (± one standard deviation) after correction for blood contribution and partial saturation was significantly lower in HCM patients relative to the control subjects (1.32 ± 0.29 vs 1.65 ± 0.26, P < .05) but not in DCM patients (1.52 ± 0.58 vs 1.65 ± 0.26). The inorganic phosphate (Pi) peak was resolved only in patients with the highest spectral quality. Myocardial pH was lower in HCM patients (n = 6) relative to control subjects (n = 4) (7.07 ± 0.07 vs 7.15 ± 0.03, P < .05). The Pi/PCr ratio was higher in DCM (n = 3) and HCM (n = 6) patients relative to control subjects (n = 4) (0.29 ± 0.06 and 0.20 ± 0.04, respectively, vs 0.14 ± 0.06; P < .05). Elevated phosphodiester signal in DCM patients correlated with 2,3‐diphosphoglycerate signal (r = .94), reflecting blood pool contamination. P‐31 spectroscopy enabled detection of abnormalities in cardiac metabolism and determination of pH in patients with HCM and DCM.