High intensity endurance exercise training increases maximal attainable O2 uptake (VO2max) and stroke volume (SV) in patients with ischaemic heart disease. To determine the mechanisms responsible for enhanced SV after training, 18 patients, 51 +/- 3 years (mean +/- SE) were studied. Patients completed 12 months of endurance exercise with a peak intensity of 89.7 +/- 2% of attainable VO2max. Attainable VO2max increased from 23 +/- 1 to 32 +/- 2 ml/kg/min (P less than 0.0001). Left ventricular function was assessed using radionuclide ventriculography. To control for afterload, haemodynamic variables were evaluated at comparable mean blood pressure (mBP). SV was increased after training both at rest (77 +/- 3 vs 81.5 +/- 5 ml; P less than 0.025) and during exercise (78 +/- 6 vs 93 +/- 6 ml; P less than 0.025) at comparable mBP. Before training, ejection fraction decreased during exercise (59 +/- 3 vs 55 +/- 3%, P less than 0.005) but increased after training from the resting level (59 +/- 3 vs 63 +/- 3%, P less than 0.025). Left ventricular end diastolic volume during exercise did not change. Thus, the results suggest that enhanced SV during exercise is, in part, due to improved left ventricular function after exercise training.