Congenital hypothyroidism is a significant issue in neonates. A variety of cardiac abnormalities have been described in cases of
severe hypothyroidism. It is commonly associated with sinus bradycardia, low QRS complexes, prolonged QT interval and
conduction blocks but may rarely cause arrhythmias. Although supraventricular arrhythmias are ordinary features of
hyperthyroidism, the aim of this report is to underline the possible etiological link between supraventricular tachycardia and
hypothyroidism. Although a few adult cases with hypothyroidism and tachyarrhythmia have been previously reported in the
literature, to our knowledge, these are the only neonatal cases reported.