Does potassium help heart rhythm?

A low blood level can cause abnormal heart rhythms, especially in people with heart disease.^[1] A 2025 trial included 1,200 people with an implanted defibrillator (ICD) and a potassium level of 4.3 mmol/L or less. Half were treated to reach 4.5 to 5.0 mmol/L with potassium supplements, a medicine (a mineralocorticoid receptor antagonist) or both, plus advice on diet. Over a median of 39.6 months, 22.7% had a dangerous heart rhythm, an unplanned hospital stay for arrhythmia or heart failure, or died, against 29.2% with standard care.^[2] In a 2024 trial of 1,690 people after heart bypass surgery, giving potassium only below 3.6 mEq/L was not worse than keeping it at 4.5 mEq/L or more. Atrial fibrillation occurred in 27.8% with the lower threshold and 26.2% with the higher one.^[3] Both trials were in heart patients under medical care, not in healthy people taking a supplement.^[2][3]