Using miRCURY LNA-miR-TSB in vivo to selectively block the mi-R31–5p/CALCR interaction, we tested causality between the miR-31–5p/CALCR interaction, atrial fibrosis, and AF development in the previously-validated Lkb1-aKD mouse model of spontaneous AF (fig. This evidence concerns the gene CALCR and atrial fibrillation.