Background: Diagnosis of heart failure with preserved ejection fraction (HFpEF) remains challenging despite the use of scores/algorithms. This study intended to assess the diagnostic value of exercise lung ultrasound (LUS) for HFpEF diagnosis. Methods: We studied two independent case-control studies of HFpEF patients and control subjects undergoing different exercise protocols: i) submaximal exercise stress echocardiography (ESE) with LUS performed by expert cardiologists (N=116, HFpEF=65.5%), and ii) maximal cycle ergometer test (CET) (N=54, HFpEF=50%) with LUS performed by unexperienced physicians shortly trained for the study. B-line kinetics (i.e. peak values and their changes from rest) were assessed Results: In the ESE cohort, the C-index (95% CI) of peak B-lines for HFpEF diagnosis was 0.985 (0.968-1.000), whereas the C-index of rest and exercise HFA-PEFF scores (i.e. including stress echo findings) were <0.90 (CI 0.823-0.949), and that of H2FPEF scores was <0.70 (CI 0.558-0.764). The C-index increase of peak B-lines on top of the above-mentioned scores was significant (C-index increase >0.090 and P-value <0.001 for all). Similar results were observed for change Blines. Peak B-line >5 (sensitivity=93.4%, specificity=97.5%) and change B-line >3 (sensitivity=94.7%, specificity=87.5%) were the best cutoffs for HFpEF diagnosis. Adding peak or change B-lines on top of HFpEF scores and BNP significantly improved diagnostic accuracy. Peak B-lines showed a good diagnostic accuracy in the LUS beginner-led CET cohort (C-index=0.713, 0.588-0.838). Conclusions: exercise LUS showed excellent diagnostic value for HFpEF diagnosis regardless of different exercise protocols/level of expertise, with additive diagnostic accuracy on top of available scores and natriuretic peptides.