– PDE1C belongs to the cyclic nucleotide phosphodiesterase family, PDE1 subfamily. Phosphodiesterases (PDEs) are a family of related phosphohydrolyases that selectively catalyze the hydrolysis of 3′ cyclic phosphate bonds in adenosine and/or guanine 3′,5′ cyclic monophosphate (cAMP and/or cGMP). They regulate the cellular levels, localization and duration of action of these second messengers by controlling the rate of their degradation. PDEs are expressed ubiquitously, with each subtype having a specific tissue distribution. These enzymes are involved in many signal transduction pathways and their functions include vascular smooth muscle proliferation and contraction, cardiac contractility, platelet aggregation, hormone secretion, immune cell activation, and they are involved in learning and memory. PDE1C has a high affinity for both cAMP and cGMP. It is expressed in several tissues, including brain and heart. As a cyclic nucleotide phosphodiesterase, PDE1C has a dual-specificity for the second messengers cAMP and cGMP.