This study used 31P nuclear magnetic resonance (NMR) spectroscopy to determine whether the magnitude and duration of myocardial reactive hyperemia (RH) reflect a commensurate derangement of myocardial high-energy phosphate (HEP) metabolism, or if coronary blood flow (CBF) and HEP metabolism are dissociated during RH. Twelve open-chest anesthetized pigs were studied during and after 24 s occlusion of the anterior descending coronary artery. CBF velocity was measured with a Doppler probe. NMR time resolution (4.8 s) was obtained by summing corresponding short blocks of data from multiple occlusions. During occlusion, phosphocreatine (PCr) declined to 65 +/- 5% (mean +/- SE) of control accompanied by increased spectral intensity of the Pi + phosphomonester region. By 20 s of reflow, HEPs had returned to control levels, but CBF was still elevated at 282 +/- 18% of control and remained elevated for an additional 53 +/- 7 s, during which 44 +/- 6% of total RH flow occurred. Therefore, the control of CBF is not closely coupled to the levels of myocardial HEPs during RH and the duration of RH does not reflect prolonged depletion of myocardial HEPs.