CRISPR-Cas9-mediated knockout of PRRX1 in human embryonic stem cells (hESCs) and morpholino-mediated knockdown of the putative PRRX1 orthologues in the zebrafish (prrx1a and prrx1b) showed that even a small modulation of PRRX1 expression may be sufficient to modulate the atrial action potential duration (APD), a hallmark of AF. Here, PRRX1 is linked to atrial fibrillation.