Background: We assessed the efficacy and safety of tadalafil, a phosphodiesterase type 5 inhibitor, in patients with heart failure with preserved ejection fraction and combined postcapillary and precapillary pulmonary hypertension., Methods: In the double-blind PASSION study (Phosphodiesterase-5 Inhibition in Patients With Heart Failure With Preserved Ejection Fraction and Combined Post- and Pre-Capillary Pulmonary Hypertension), patients with heart failure with preserved ejection fraction and combined postcapillary and precapillary pulmonary hypertension were randomized 1:1 to receive tadalafil at a target dose of 40 mg or placebo. The primary end point was the time to the first composite event of adjudicated heart failure hospitalization or all-cause death. Secondary end points included all-cause mortality and improvements in New York Heart Association functional class or ≥10% improvement in 6-minute walking distance from baseline., Results: Initially targeting 372 patients, the study was terminated early because of disruption in study medication supply. At that point, 125 patients had been randomized (placebo: 63; tadalafil: 62,). Combined primary end-point events occurred in 20 patients (32%) assigned to placebo and 17 patients (27%) assigned to tadalafil (hazard ratio, 1.02 [95% CI, 0.52-2.01]; P =0.95). There was a possible signal of higher all-cause mortality in the tadalafil group (hazard ratio, 5.10 [95% CI, 1.10-23.69]; P =0.04). No significant between-group differences were observed in other secondary end points. Serious adverse events occurred in 29 participants (48%) in the tadalafil group and 35 (56%) in the placebo group., Conclusions: The PASSION trial, terminated prematurely due to study medication supply disruption, does not support tadalafil use in patients with heart failure with preserved ejection fraction and combined postcapillary and precapillary pulmonary hypertension, with potential safety concerns and no observed benefits in primary and secondary end points., Registration: URL: https://www.clinicaltrialsregister.eu/; Unique identifier: 2017-003688-37. URL: https://drks.de; Unique identifier: DRKS -DRKS00014595., Competing Interests: Dr Hoeper has received fees for lectures and/or consultations from Acceleron, Actelion, AOP Health, Bayer, Ferrer, GossamerBio, Janssen, Keros, and MSD. Max Wissmüller has received lecture fees from Janssen. Hanno Leuchte has received fees for consultations and/or lectures from Acceleron, Jansse-Cilag, Bayer, Boehringer-Ingelheim, Ferrer, MSD, and Pfizer. Michael Halank has received fees for lectures and/or consultations from AstraZeneca, Janssen-Cilag, and MSD. In addition, he has received support for attending meetings and/or travel from AOP Health and Janssen-Cilag. Hans-Jürgen Seyfarth has received fees for lectures and/or consultations from Janssen-Cilag and MSD. Stephan Baldus has received fees for lectures and/or consultations from Abbott, Edwards, Jenavalve, AstraZeneca, Bayer, Daiicho Sankyo, and Amgen, as well as research grants from Abbott, AstraZeneca, and Daiichi Sankyo. Johann Bauersachs has received fees for lectures and/or consultations from Amgen, AstraZeneca, Bayer, BMS, Boehringer Ingelheim, Cardior, Corvia, CVRx, Edwards, Norgine, Novartis, Pfizer, Roche and Vifor. In addition, institutional grants have been provided by Abiomed, CVRx, Norgine, Roche, and Zoll. He holds patents for microRNA and downstream targets for diagnostics and therapeutic purposes (PCT/EP2007/008772 and PCT/EP2009/051986). Michael Böhm is supported by the Deutsche Forschungsgemeinschaft (German Research Foundation; TTR 219, project No. 322900939) and reports personal fees from Abbott, Amgen, AstraZeneca, Bayer, Boehringer Ingelheim, Cytokinetics, Medtronic, Novartis, ReCor, Servier and Vifor. Hossein-Ardeschir Ghofrani has received honoraria for consultations and/or speaking at conferences from Bayer HealthCare AG, Actelion, Encysive, Pfizer, Ergonex, Lilly, and Novartis. He is member of the Advisory Board for Acceleron, Bayer HealthCare AG, Pfizer, GSK, Actelion, Lilly, Merck, Encysive, and Ergonex. He has also received governmental grants from the German Research Foundation, Excellence Cluster Cardiopulmonary Research, State Government of Hessen, and the German Ministry for Education and Research. Stavros Konstantinides reports personal lecture/advisory fees and research grants to his institution from Bayer AG, Boston Scientific, Daiichi-Sankyo, LumiraDx, and Penumbra, as well as personal lecture/advisory fees from MSD and Pfizer–Bristol-Myers Squibb. Karen M. Olsson has received fees for lectures and/or consultations from Acceleron, Actelion, Bayer, Ferrer, GSK, Janssen, MSD, Pfizer, and United Therapeutics. Rolf Wachter has received fees for lectures and/or consultation from AstraZeneca, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, Daiichi Sankyo, Medtronic, Novartis, Pfizer, Pharmacosmo, Sciarc, Servier, and Vifor. His institution has received research grants from Deutsche Forschungsgemeinschaft, Bundesministerium für Bildung und Forschung, European Union, and Medtronic. Carolyn S.P. Lam is supported by a Clinician Scientist Award from the National Medical Research Council of Singapore; has received research support from NovoNordisk and Roche Diagnostics; has served as consultant or on the Advisory Board/ Steering Committee/ Executive Committee for Alleviant Medical, Allysta Pharma, AnaCardio AB, Applied Therapeutics, AstraZeneca, Bayer, Biopeutics, Boehringer Ingelheim, Boston Scientific, Bristol Myers Squibb, CardioRenal, Cytokinetics, Darma Inc, EchoNous Inc, Eli Lilly, Impulse Dynamics, Intellia Therapeutics, Ionis Pharmaceutical, Janssen Research & Development LLC, Medscape/WebMD Global LLC, Merck, Novartis, Novo Nordisk, Prosciento Inc, Quidel Corp, Radcliffe Group Ltd, Recardio Inc, ReCor Medical, Roche Diagnostics, Sanofi, Siemens Healthcare Diagnostics, and Us2.ai; and serves as cofounder and non–executive director of Us2.ai. Stephan Rosenkranz has received fees for lectures and/or consultations from Abbott, Acceleron, Actelion, Aerovate, AOP, AstraZeneca, Bayer, Boehringer-Ingelheim, Edwards, Ferrer, Gossamer, Janssen, MSD, and United Therapeutics. His institution has received research grants from Actelion, AstraZeneca, Bayer, Janssen, and Lempo. The other authors report no conflicts.