Increased circulating proinflammatory cytokines, including IL-1β, correlate with AF progression in humans, promote arrhythmias in mice, and specifically depress cardiomyocyte function and cytosolic calcium release from the SR.52–54 We found that human pluripotent stem cell atrial cardiomyocytes stimulated with either human IL-1β or IL-6 had decreased calcium transient amplitude compared with untreated human pluripotent stem cell atrial cardiomyocytes (Figure 6F). Here, IL6 is linked to atrial fibrillation.