Thus, we transduced human isolated atrial myocytes from Ctl and AF patients with genetically encoded FRET-based biosensors for cytosolic cAMP (Epac1-camps), sarcolemmal cAMP (pm-Epac1) and cAMP in the vicinity of the RyR2 (Epac1-JNC). Here, RYR2 is linked to atrial fibrillation.