We present a case of flecainide-induced hyponatremia in a 67-year-old woman who was treated for paroxysmal atrial tachycardia. She developed dizziness after starting flecainide and was found to be hyponatremic with a sodium level of 122 mmol/L (decreased from 136 mmol/L). Work-up failed to reveal other causes of hyponatremia. She was not on diuretics, laxatives, or herbal medications. After discontinuation of flecainide, her symptoms and sodium levels improved. Hyponatremia is a previously unrecognized entity as an adverse effect of flecainide. We will discuss the clinical presentation, lab findings, and a possible explanation for this patient's unusual reaction to flecainide.