May play a role in the maintenance of heart function mediated, at least in part, through cAMP-binding. May play a role in the regulation of KCNK2-mediated current amplitude (By similarity). Expressed first preferentially in atrium and later also in the subepicardial compact layer of the ventricles. Expression was first detected at HH stage 10 and was initially expressed throughout the heart. With heart looping at HH stage 11, expression was restricted to the atrial compartment and absent from the presumptive ventricular segments. The atrial-specific expression was still observed at stage 17. During HH stages 17-24, increased expression in the subepicardial compact layer was seen. At HH stage 30, expression was seen intensely in the whole myocardium with the exception of the outflow tract. Belongs to the popeye family.