The postpartum period can unmask LQTS. We described a case of 22-year-old woman with episode of lost of consciousness 6 months after delivery. Holter monitoring showed episodes of QTc prolongation, max. QTc - 618 ms, medium QTc - 538 ms with different morphology types of T wave. Beta-blocker (BB) therapy (metoprolol was initiated) and titrated up to 200 mg daily. The patient was out of symptoms. After 2 years during the second pregnancy she reduced BB to 50 mg/day. In the postpartum period, 3 months after delivery she had syncopal episodes. Holter monitoring showed polymorphic ventricular tachycardia. The cardioverter-defibrillator was implanted.