Left ventricular function (LVEF) deteriorates during incremental exercise (GXT) in patients with ischemia (+ISCH). Left ventricular (LV) functional response during steady-state exercise, typical of that used in exercise training, are unknown. We compared LVEF in patients with documented coronary heart disease (CHD) who either had (+) or did not have (-) ISCH, and in healthy volunteers (CONTROL) during GXT and steady state. First pass RNA was performed during upright cycle GXT at rest (R), at the ventilatory threshold (VT), and at maximal exercise (Max); and during steady state at the workload associated with VT after 10, 20, and 30 min of exercise. RNA allowed measurement of ejection fraction (EF) and wall motion (WM); ISCH was mild, angina being relieved by momentary reductions in workload during steady state. Although +ISCH demonstrated the expected deterioration in LV function during GXT (decreased EF, abnormal WM)(EF = 58 to 56 to 54%), there was no evidence for progressive deterioration of LV function during steady state despite the presence of mild ISCH (56 to 56 to 54 to 54%). In -ISCH and CONTROL there were normal responses of EF during GXT (43 to 51 to 51% and 59 to 65 to 61%) and steady state (43 to 51 to 53 to 51% and 59 to 65 to 68 to 69%). We conclude that mild ischemia may be tolerated during steady-state exercise at levels consistent with exercise training without progressive deterioration of LV function.