Expression of IP3R type 2 (IP3R2), the most abundant IP3R isoform in cardiac tissue (20, 39), is at least six times greater in the atria compared with the ventricle (20), and IP3R expression is upregulated in both human patients with chronic atrial fibrillation (AF) (46) and canine AF models (47). The gene discussed is ITPR2; the disease is atrial fibrillation.