Hyperkalaemia is a common co-morbidity in patients with heart failure with reduced ejection fraction (HFrEF). Whether it affects the use of renin-angiotensin-aldosterone system inhibitors and thereby negatively impacts outcome is unknown. Therefore, we investigated the association between potassium and uptitration of angiotensin-converting enzyme inhibitors (ACEi)/angiotensin receptor blockers (ARB) and its association with outcome.