["In the heart, β<sub>1</sub>-adrenergic signaling involves cyclic adenosine monophosphate (cAMP) acting via both protein kinase-A (PKA) and 'exchange protein directly activated by cAMP' (Epac): a guanine nucleotide exchange factor for the small GTPase Rap1. Inhibition of Epac-Rap1 signaling has been proposed as a therapeutic strategy for both cancer and cardiovascular disease. However, previous work suggests that impaired Rap1 signaling may have detrimental effects on cardiac function. The aim of the present study was to investigate the influence of Epac2-Rap1 signaling on the heart using both in vivo and in vitro approaches.", 'Impaired Epac2 signaling induced early afterdepolarization arrhythmias in ventricular myocytes. The underlying mechanism involved an increase in mitochondrial reactive oxygen species (ROS) and activation of the late sodium current (INa<sub>late</sub>). Arrhythmias were blocked by inhibition of INa<sub>late</sub> or the mitochondria-targeted antioxidant mitoTEMPO. In vivo, inhibition of Epac2 caused ventricular tachycardia, torsades de pointes and sudden death. The in vitro and in vivo effects of Epac2 inhibition were mimicked by inhibition of geranylgeranyltransferase-1, which blocks interaction of Rap1 with downstream targets.', 'Our findings show for the first time that Rap1 acts as a negative regulator of mitochondrial ROS production in the heart and that impaired Epac2-Rap1 signaling causes arrhythmias due to ROS dependent activation of INa<sub>late</sub>. This has implications for the use of chemotheraputics that target Epac2-Rap1 signaling. However, selective inhibition of INa<sub>late</sub> provides a promising strategy to prevent arrhythmias caused by impaired Epac2-Rap1 signaling.'] Does epac2-Rap1 signaling regulate reactive oxygen species production and susceptibility to cardiac arrhythmias?