Six patients with ischemic heart disease who had exercised intensely for longer than 1 yr appeared to have a disproportionally high capacity for endurance exercise relative to V̇(O2max). They were compared with healthy runners of the same age (mean 55 yr) with similar training programs (6-12 km/day, 5 day/wk). The trained patients had a significantly (P <0.05) lower maximal cardiac output (-17%) and V̇(O2max) (-18%, 37 vs. 45 ml·kg-1·min-1). Despite their lower V̇(O2max) the trained patients were able to run 8 km at the same speed as the normal runners (~189 m/min). The trained patients' ability to keep pace with the normal subjects was apparently due to a very high lactate threshold (LT) relative to V̇(O2max). The patients' LT (lactate 1 mM above base line) occurred at a treadmill running speed of 176 m/min, which elicited 100% of their V̇(O2max), compared with a LT at 178 m/min and 84% of V̇(O2max) in the normal subjects (P <0.01). Our results show that some individuals with V̇(O2max) limited by impaired cardiac function can undergo adaptations to training that enable them to maintain close to a metabolic steady state during exercise that elicits V̇(O2max).