Pathogenic variants ofHECW2have been reported in cases of neurodevelopmental disorder with hypotonia, seizures, and absent language (NDHSAL; OMIM #617268). A novelHECW2variant (NM_001348768.2:c.4343 T > C,p.Leu1448Ser) was identified in an NDHSAL infant with severe cardiac comorbidities. The patient presented with fetal tachyarrhythmia and hydrops and was postnatally diagnosed with long QT syndrome. This study provides evidence thatHECW2pathogenic variants can cause long QT syndrome along with neurodevelopmental disorders.