The improvement of exercise capacity due to exercise training in heart failure has been associated with peripheral adaptation, but the contribution of cardiac responses is less clear. We sought the extent to which the improvement of functional capacity in patients undergoing exercise training for heart failure was related to myocardial performance. Thirty-seven patients (35 men, age 64 +/- 11) with symptomatic heart failure and left ventricular ejection fraction < or = 35% (29 +/- 9%) were studied during a 16-week exercise training program. LV function was assessed by resting and exercise 2D-echocardiography, tissue Doppler derived myocardial strain, and strain rate. Peak oxygen consumption (VO2) and LV function were measured at baseline and follow-up, and the contribution of LV function at baseline and its response to training to the change of each parameter was sought. Baseline peak VO2 (12.4 +/- 4.6) increased by 9% at 8 weeks (13.5 +/- 4.2, P = 0.26), and by 21% at 16 weeks (15.0 +/- 4.9, P < 0.001). Although there were no overall changes in myocardial parameters in this study, change in peak VO2 at 16 weeks was significantly correlated with baseline strain (r = 0.51, P = 0.003) and the improvement of strain at 8 weeks (r = 0.44, P = 0.01), independent of baseline functional capacity and clinical variables. Thus, change in peak VO2 following 16 weeks exercise training is related to myocardial function at baseline.