Hydrolyzes cAMP to 5'-AMP. Plays an important regulatory role in modulating the intracellular concentration of cAMP, thereby influencing cAMP-dependent processes. Can also hydrolyze cGMP. a nucleoside 3',5'-cyclic phosphate + H2O = a nucleoside 5'-phosphate + H(+) 3',5'-cyclic AMP + H2O = AMP + H(+) 3',5'-cyclic GMP + H2O = GMP + H(+) Binds 2 Fe(2+) ions per subunit. Activated by iron and manganese. Belongs to the cyclic nucleotide phosphodiesterase class-III family.