ATP content [ATP] and fraction of rod-shaped myocytes (Rrod) were measured in ventricular myocytes isolated from the rat heart. [ATP] (nmol (10(6) cells)-1) and Rrod (%) were 72.0 and 60.5, respectively, and significantly reduced to 18.8 and 41.8 by no-flow ischemia for 30 min. Reperfusion for 15 min with cardioplegic solutions restored [ATP] of rod-shaped myocytes to the control level.