Improvement in left ventricular (LV) systolic reserve, including exertional increase in global longitudinal strain (GLS), may contribute to the clinical benefit from therapeutic interventions in heart failure with preserved ejection fraction (HFpEF). However, GLS is an afterload-dependent parameter, and its measurements may not adequately reflect myocardial contractility recruitment with exercise. The estimation of myocardial work (MW) allows correction of GLS for changing afterload. We sought to investigate the associations of GLS and MW parameters with the response of exercise capacity to spironolactone in HFpEF.We analysed 114 patients (67 ± 8 years) participating in the STRUCTURE study (57 randomized to spironolactone and 57 to placebo). Resting and immediately post-exercise echocardiograms were performed at baseline and at 6-month follow-up. The following indices of MW were assessed: global work index (GWI), global constructive work (GCW), global wasted work, and global work efficiency. The amelioration of exercise intolerance at follow-up in the spironolactone group was accompanied by a significant improvement in exertional increase in GCW (P = 0.002) but not in GLS and other MW parameters. Increase in exercise capacity at 6 months was independently correlated with change in exertional increase in GCW from baseline to follow-up (β = 0.24; P = 0.009) but not with GLS (P = 0.14); however, no significant interaction with the use of spironolactone on peak VO2 was found (P = 0.97).GCW as a measure of LV contractile response to exertion is a better determinant of exercise capacity in HFpEF than GLS. Improvement in functional capacity during follow-up is associated with improvement in exertional increment of GCW.