I studied the influence of insulin upon the consumption of glycogen contained in the heart muscule and of glucose or laevulose in the perfused liquid by the heart of Japanese toad, Bufo vulgaris japonicus and obtained following results. 1) Isolated from the body and artificially perfused heart of toad with Ringer-Locke solution, does not use of glucose or laevulose in the solution. 2) If added insulin in the perfused liquid, glucose in it is consumed pretty well by the heart e. g. 11.85 mg. per gr. of heart muscle in an hour. Glycogen content in the heart always diminishes. Diminished amount of glycogen is nearly proportional to the work done by the heart. There is reason to believe that glucose in the perfused liquid turns at first to glycogen and then is able to use by the heart. 3) Laevulose in the perfused liquid even after adding of insulin is not used by the heart at all. Work of heart in this case always diminishes.