OBJECTIVES: This study investigated 1-year incidence and predictors of dyskalemia (dysK) and its outcome associations in heart failure with preserved ejection fraction (HFpEF), HF with mid-range EF (HFmrEF), and HF with reduced EF (HFrEF). BACKGROUND: DysK in real-world HF is insufficiently characterized. Fear of dyskalemia may lead to underuse or underdosing of renin-angiotensin-aldosterone system inhibitors. METHODS: Patients enrolled in the SwedeHF (Swedish Heart Failure) Registry from 2006 to 2011 in Stockholm, Sweden were included in the analyses. Multivariate Cox regression analysis identified independent predictors of dysK within 1 year. Time-dependent Cox models assessed outcomes associated with incident dysK (all-cause death, HF, and other cardiovascular disease [CVD] hospitalizations) within 1 year from baseline. RESULTS: Of 5,848 patients, 24.4% experienced hyperkalemia (hyperK [K >5.0 mmol/l]) at least once, and 10.2% had moderate or severe hyperK (K >5.5 mmol/l). Adjusted risk of moderate or severe hyperK was highest in HFpEF and HFmrEF. Similarly, 20.3% of patients had at least one episode of hypokalemia (hypoK [<3.5 mmol/l]), and 3.7% had severe hypoK (<3.0 mmol/l). Adjusted risk of any hypoK was highest in HFpEF. Independent predictors of both hyperK and hypoK were sex, baseline potassium and estimated glomerular filtration rate, low hemoglobin, chronic obstructive pulmonary disease (COPD), inpatient status, and higher New York Heart Association functional class. Incident dysK was associated with increased risk of mortality. Furthermore, hypoK was associated with increased CVD hospitalizations (HF-related excluded). There was no association between dysK and HF hospitalization risk, regardless of EF. CONCLUSIONS: DysK is common in HF and is associated with increased mortality. Risk of moderate or severe hyperK was highest in HFpEF and HFmrEF, whereas risk of hypoK was highest in HFpEF. HF severity, low hemoglobin, COPD, baseline high and low potassium, and low eGFR were relevant predictors of dysK occurrence. Copyright © 2019 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.