Introduction: Supraventricular paroxysmal tachycardia (SPT) in a fetus and newborn represent a group of tachycardia with different mechanism of origin, clinical symptoms and differen prognosis. If SPT occurs during the intrauterine development it may results in severe multiorgan failure. These conditions may be treated during the pregnancy. If the therapy fails, abortion is indicated. If manifested at the newborn age, the extent of complications is directly proportional to the duration of paroxysms of tachycardia. Patients and methods: The authors present 4 patients determined prenatally (2 patients) and postnatally (2 patients) hospitalized at the Ward for Pathological Newborns, 1st Clinic of Medical Faculty, UK in Bratislava in the period of October 2002 till November 2003. Results: In two patients SPT became manifest prenatally in an intrauterine picture of multiorgan failure and hydrops of the fetus on the basis of a severe heart failure. In two patients it became manifest after birth with a typical picture of reentry tachycardia. It was manageable by vagus maneuvers and administration of adenosine. The patients were gradually treated with a complex anti-arrhythmic therapy. Conclusion: The authors discuss the modes of intrauterine modulation of the patient’s condition in severe tachyarrhythmia. The attention is drawn to the need of termination of pregnancy in unsuccessful medication treatment of tachyarrhythmia. When manifested in the newborn period of life, various complications as well as prognosis of the patients are directly proportional to the duration of paroxysms of tachycardia.

        Key words: reentry tachycardia, newborn, complications