Plays a role in signal transduction by regulating the intracellular concentration of cyclic nucleotides cAMP and cGMP (PubMed:15800654). Catalyzes the hydrolysis of both cAMP and cGMP to 5'-AMP and 5'-GMP, respectively (By similarity). 3',5'-cyclic GMP + H2O = GMP + H(+) 3',5'-cyclic AMP + H2O = AMP + H(+) Binds 2 divalent metal cations per subunit. Site 1 may preferentially bind zinc ions, while site 2 has a preference for magnesium and/or manganese ions. Inhibited by 3-isobutyl-1-methylxanthine (IBMX), zaprinast and dipyridamole. cGMP acts as an allosteric activator (By similarity). Expressed in testis and developing spermatoza. The tandem GAF domains bind cGMP, and regulate enzyme activity. The binding of cGMP stimulates enzyme activity. Mice live well and have no impaired fertility. They do however display reduced sperm concentration, rate of forward progression and percentage of live spermatozoa. Pre-ejaculated sperm display increased premature/spontaneous capacitance. Belongs to the cyclic nucleotide phosphodiesterase family.