Fluorine NMR spectroscopy of sequestered perfluorocarbon emulsion has been used to measure myocardial oxygen tension. This novel application provides a rapid noninvasive assessment of changes in oxygen tension in response to ischemia and reperfusion. Rats were predosed with Oxypherol‐ET (emulsion of perfluorotributylamine). Following vascular clearance of the emulsion the heart was excised and perfused using the Langendorff retrogradetechnique. ¹⁹F spin‐lattice relaxation time measurements provided an accurate estimate of myocardial pO₂. Using a two‐point determination with a time resolution of 1 s, the loss of oxygen was found to be complete within 40 s of the onset of global ischemia. The fall in oxygen tension correlated closely with an observed loss of ventricular pressure. Magnetic resonance imaging showed that perfluorocarbon was distributed throughout the heart; thus, this reporter molecule provides a global measurement of oxygen tension.