O2 consumption in isolated cardiac myocyte declines with age. O2 consumption in isolated cardiac myocytes from young and old rats was monitored using a Clark type oxygen electrode (Yellow Springs Instruments, Yellow Springs, Ohio). Cardiac myocytes (1×106) were added to 3 ml of Krebs-Henseleit buffer supplemented with 20 mM glucose, pH 7. 4, that had been pre-equilibrated to 37°C, and oxygen consumption was monitored for at least 15 min (25). Results show that O2 consumption, an indicator of cellular metabolic rate, declines sharply with age. Results are expressed as mean ± SE for cells from young rats (n=5) and the mean ± SE (n=5) for cells from old rats.