The interventricular site has been proposed as one of the sites for the myocyte cell death with aging and thereby enhancing the possibility of ventricular dysfunction with aging. Variations in lactate dehydrogenase (LDH), a key glycolytic regulatory enzyme along with its isomers were used as indices to evaluate the anaerobic capacity of the interventricular septum (IVS) in 2-month-old (young) and 12-month-old (middle-aged) rats trained to swim at 25°C (cold, C) and 35°C (thermo neutral, N) temperatures. Blood lactate (La) and LDH along with its isoenzymes in the IVS were assessed and compared with untrained and sedentary rats. Increased septal and heart weight was indicative of age-related hypertrophy accompanied by increased septal thickness. Elevated total LDH activity was evident in both the trained groups in the young. The middle-aged animals exhibited lesser variations in LDH and, H and M subunits. The data suggest an efficient adaptability of the IVS of young rats to physical training in contrast to a poor response by the IVS of middle-aged animals.