TTN and hydrops fetalis: The aim of this study was to determine if TTN antisense transcripts play a role in alternative splicing of TTN.<h4>Methods and results</h4>RNA-sequencing and RNA in situ hybridization (ISH) of cardiac tissue from heart failure (HF) patients, unused donor hearts, and human iPS-derived cardiomyocytes (iPS-CMs) were used to determine the expression and localization of TTN NATs.