The importance of extracellular glucose in the maintenance of performance of the heart of the American eel (Anguilla rostrata Le Sueur (L.) Under anoxia was assessed under a variety of experimental conditions. Ventricular strips, electrically paced at 36 bpm, in N(2)-gassed medium maintained the imposed pace rate and generated approximately 25% of the initial twitch force of contraction for at least 60 min when glucose was present in the medium. But ventricular strips challenged without glucose in the medium failed to maintain the pacing rate within 5-10 min. Isolated and intact, perfused hearts maintained pressure and followed an imposed pace rate of 24 bpm for at least 2 hr, under anoxic conditions, if glucose was present in the medium. But without glucose in the medium isolated hearts failed within 30 min. Endogenous glycogen stores were utilized in hearts perfused with medium containing NaCN to impair oxidative phosphorylation. The presence of glucose in the medium did not protect against glycogen mobilization. The data indicate that exogenous glucose is necessary to maintain performance under anoxia at high workloads and physiological Ca(2+) levels. Finally, ventricular strips treated with NaCN and forced to contract at 24 bpm lost 70% of initial twitch force. Increasing extracellular Ca(2+) concentration stepwise from 1.5 to 9.5 mM restored twitch force to approximately 50% of the initial level and this response was not dependent on exogenous glucose. However, glucose was required to maintain resting tension even under normoxic conditions in the face of a Ca(2+) challenge.