Potassium is the most important intracellular cation in a humans body. Potassium gradient between the intracellular fluid to the extra cellular fluid is crucial for normal nerve-muscle activity. Hypokalemia is a frequent abnormality among patients, exposing them to fatigue and arrhythmia. Understanding the pathophysiology of hypokalemia may help the clinician to treat it properly. The approach to the patient with hypokalemia is presented through the description of a 25-year-old woman who was admitted to the department due to palpitation and hypokalemia. A simple primary investigation is suggested in these cases.