Indeed, inhibition of cAMP-dependent protein kinase A (PKA) induces substantial bradycardia in cardiac pacemaker cells (Vinogradova et al., 2006), and independent of either PDE3 or PDE4, induces sinoatrial bradycardia in the rat and mouse (Galindo‐Tovar and Kaumann, 2008). Here, PDE4A is linked to Bradycardia.