Cooper LB, Benson L, Mentz RJ, et al. - Researchers utilized the Swedish Heart Failure Registry, to define the optimal range of potassium among patients with heart failure and reduced ejection fraction (< 40%). For this purpose, they examined the link between baseline potassium level and short-and long-term outcomes. In uni- and multivariable stratified and restricted cubic spline Cox regressions, they evaluated the link between baseline potassium level and all-cause death at 30 days, 12 months, and maximal follow-up. Findings revealed a U-shaped link between potassium and mortality, with an optimal potassium value of 4.2 mmol/L. The association of hypokalaemia with increased long-term mortality and that of hyperkalaemia with increased short-term mortality was revealed following multivariable adjustment.