Aims Pulmonary congestion during exercise assessed by lung ultrasound predicts negative outcome in patients with heart failure with preserved ejection fraction (HFpEF). We aimed at assessing predictors of exercise-induced pulmonary B-lines in HFpEF patients. Methods and results Eighty-one I-II NYHA class HFpEF patients (65.0 ± 8.2 y/o, 56.8% females) underwent standard and strain echocardiography, lung ultrasound, and natriuretic peptide assessment during supine exercise echocardiography (baseline and peak exercise). Peak values and their changes were compared in subgroups according to exercise lung congestion grading (peak B-lines >10 or ≤10). Exercise elicited significant changes for all echocardiographic parameters in both subgroups [39/81 (48.1%) with peak B-lines >10; 42/81 (51.9%) with B-lines ≤10]. Peak values and changes of E-wave (and its derived indices) were significantly higher in patients with >10 peak B-lines compared with those with ≤10 B-line (all P-values <0.03), showing significant correlation with peak B-lines for all parameters; concomitantly, global longitudinal strain (GLS) and global strain rate (GSR) during systole (GSRs), early (GSRe) and late (GSRa) diastole, and isovolumic relaxation (GSRivr) were reduced in patients with B-lines >10 (all P-values <0.05), showing a negative correlation with peak B-lines. By adjusted linear regression analysis, peak and change diastolic parameters (E-wave, E/e0, GSRivr, and E/GSRivr) and peak GLS were individually significantly associated with peak B-lines. By covariate-adjusted multivariable model, E/e0 and GSRa at peak exercise were retained as independent predictors of peak B-lines, with substantial goodness of fit of model (adjusted R 2 0.776). Conclusions In HFpEF, development of pulmonary congestion upon exercise is mostly concomitant with exercise-induced worsening of diastolic function.