We report studies of the effect of ischemia on the metabolic activity of the intact perfused lung and its restoration after a period of reperfusion. Two groups of rat lungs were studied using hyperpolarized 1-13C pyruvate to compare the rate of lactate labeling differing only in the temporal ordering of ischemic and normoxic acquisitions. In both cases, a several-fold increase in lactate labeling was observed immediately after a 25-min ischemia event as was its reversal back to the baseline after 30–40 min of resumed perfusion (n = 5, p < 0.025 for both comparisons). These results were corroborated by 31P spectroscopy and correspond well to measured changes in lactate pool size determined by 1H spectroscopy of freeze-clamped specimens. Copyright © 2012 John Wiley & Sons, Ltd.