Background: Pulmonary transit time (PTT) from first-pass perfusion imaging is a novel parameter to evaluate hemodynamic congestion by cardiac magnetic resonance (cMR). We sought to evaluate the additional prognostic value of PTT in heart failure with reduced ejection fraction over other well-validated predictors of risk including the Meta-Analysis Global Group in Chronic Heart Failure risk score and ischemic cause. Methods: We prospectively followed 410 patients with chronic heart failure with reduced ejection fraction (61±13 years, left ventricular (LV) ejection fraction 24±7%) who underwent a clinical cMR to assess the prognostic value of PTT for a primary endpoint of overall mortality and secondary composite endpoint of cardiovascular death and heart failure hospitalization. Normal reference values of PTT were evaluated in a population of 40 asymptomatic volunteers free of cardiovascular disease. Results PTT was significantly increased in patients with heart failure with reduced ejection fraction as compared to controls (9±6 beats and 7±2 beats, respectively, P<0.001), and correlated not only with New York Heart Association class, cMR-LV and cMR-right ventricular (RV) volumes, cMR-RV and cMR-LV ejection fraction, and feature tracking global longitudinal strain, but also with cardiac output. Over 6-year median follow-up, 182 patients died and 200 reached the secondary endpoint. By multivariate Cox analysis, PTT was an independent and significant predictor of both endpoints after adjustment for Meta-Analysis Global Group in Chronic Heart Failure risk score and ischemic cause. Importantly in multivariable analysis, PTT in beats had significantly higher additional prognostic value to predict not only overall mortality (χ 2to improve, 12.3; hazard ratio, 1.35 [95% CI, 1.16-1.58]; P<0.001) but also the secondary composite endpoints (χ 2to improve=20.1; hazard ratio, 1.23 [95% CI, 1.21-1.60]; P<0.001) than cMR-LV ejection fraction, cMR-RV ejection fraction, LV-feature tracking global longitudinal strain, or RV-feature tracking global longitudinal strain. Importantly, PTT was independent and complementary to both pulmonary artery pressure and reduced RV ejection fraction<42% to predict overall mortality and secondary combined endpoints. Conclusions: Despite limitations in temporal resolution, PTT derived from first-pass perfusion imaging provides higher and independent prognostic information in heart failure with reduced ejection fraction than clinical and other cMR parameters, including LV and RV ejection fraction or feature tracking global longitudinal strain. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03969394.