TNNI3 and atrial fibrillation: T-Box Transcription Factor 5 (TBX5) is critical for determining ventricular versus atrial cell fate (15, 66) and its expression has been linked to the expression levels of multiple genes for proteins we found differentially expressed in AF, including MYH6 and 7; Titin, MYL2, TNNI3, and TPM 1 and 2 (66–68).