Cardiac glycogen, both free and bound, was determined in rats at two stages of acute anoxia and six stages of recovery from anoxia. The glycogen was subjected to ß amylase digestion to obtain the limit dextrin of each sample. Free and bound cardiac glycogen are both depleted by anoxia. Resynthesis is rapid, control levels being restored within 40–60 minutes. The overshoot in total glycogen after anoxia is shown to be due to the free glycogen alone. Free and bound glycogen exhibit structural differences during anoxia and during recovery from anoxia. Branching activity during resynthesis is complete for free glycogen within 1 hour but the bound glycogen shows internal transglucosidation that continues for more than 3 hours but less than 15 hours. The data reveal that the structure of glycogen is a reflection of the physiological state of the animal and that free and bound glycogen may have a real physiological significance.