serum potassium

Potassium is an electrically charged mineral that the heart relies on to fire and recover its beats. The body keeps blood potassium within a narrow band, because both too little and too much can disturb the heart's electrical rhythm — sometimes dangerously.

Inside heart cells, potassium movements help generate each electrical impulse and reset the cell afterward. When blood potassium drops too low (hypokalemia) or climbs too high (hyperkalemia), these electrical events misfire, which can produce abnormal rhythms ranging from extra beats to life-threatening ventricular arrhythmias and even cardiac arrest.

Potassium levels are routinely checked in heart patients because many common cardiac drugs — diuretics, ACE inhibitors, and others — push the level up or down, and because kidney problems impair its control. Severe abnormalities can show characteristic ECG changes, and dangerous values are treated promptly to protect the heart.