Potassium is a key electrolyte inside cells that is critical for heart rhythm and muscle function. Normal range: 3.5–5.0 mEq/L.

What this means:

• Low potassium: Can cause weakness or abnormal heart rhythms

• High potassium: Can affect heart rhythm and, at high levels, be dangerous

For healthy individuals:

Levels are usually stable. Monitoring is important if you have kidney disease or take certain medications.