OBJECTIVES This study sought to evaluate the incidence, the predictors, and the associations with outcomes of changes in ejection fraction (EF) in heart failure (HF) patients. BACKGROUND EF determines therapy in HF, but information is scarce about incidence, determinants, and prognostic implications of EF change over time. METHODS Patients with amp;gt;= 2 EF measurements were made in the Swedish Heart Failure Registry were categorized as heart failure with preserved ejection fraction (HFpEF) (EF amp;gt;= 50%), heart failure with midrange ejection fraction (HFmrEF) (EF 40% to 49%), or heart failure with reduced ejection fraction (HFrEF) (EF amp;lt;40%). Changes among categories were recorded, and associations among EF changes, predictors, and all-cause mortality and/or HF hospitalizations were analyzed using logistic and Cox regressions. RESULTS Of 4,942 patients at baseline, 18% had HFpEF, 19% had HFmrEF, and 63% had HFrEF. During follow-up, 21% and 18% of HFpEF patients transitioned to HFmrEF and HFrEF, respectively; 37% and 25% of HFmrEF patients transitioned to HFrEF and HFpEF, respectively; and 16% and 10% of HFrEF patients transitioned to HFmrEF and HFpEF, respectively. Predictors of increased EF included use of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, female sex, cases of less severe HF, and comorbidities. Predictors of decreased EF included diabetes, ischemic heart disease, and cases of more severe HF. Increased EF was associated with a lower risk (hazard ratio [HR]: 0.62; 95% confidence interval [CI]: 0.55 to 0.69) and decreased EF with a higher risk (HR: 1.15; 95% CI: 1.01 to 1.30) of mortality and/or HF hospitalizations. Prognostic implications were most evident for transitions to and from HFrEF. CONCLUSIONS Increases in EF occurred in one-fourth of HFrEF and HFmrEF patients, and decreases occurred in more than one-third of patients with HFpEF and HFmrEF. EF change was associated with a wide range of important clinical, treatment, and organizational factors as well as with outcomes, particularly transitions to and from HFrEF. (C) 2019 Published by Elsevier on behalf of the American College of Cardiology Foundation.