It has been previously shown that AF induces ROS production in various cancer cells by inhibiting TrxR1, and it is this excessive ROS production that is thought to be responsible for AF-induced cell death.22, 23, 24 We hypothesized that expression of the cysteine protease inhibitor CST1 contributes to the regulation of AF-induced ROS production and cell death in CRC cells. Here, CTSB is linked to atrial fibrillation.