PDE1 (phosphodiesterase type 1) is a phosphodiesterase enzyme also known as calcium- and calmodulin-dependent phosphodiesterase. It is one of the 11 families of phosphodiesterase (PDE1-PDE11). PDE1 has three subtypes, PDE1A, PDE1B and PDE1C which divide further into various isoforms. The various isoforms exhibit different affinities for cAMP and cGMP.