Hydrolyzes the second messenger 3',5'-cyclic AMP (cAMP), which is a key regulator of many important physiological processes. Efficiently hydrolyzes cAMP. 3',5'-cyclic AMP + H2O = AMP + H(+) Binds 2 divalent metal cations per subunit. Site 1 may preferentially bind zinc ions. Binds 2 divalent metal cations per subunit (By similarity). Site 2 has a preference for magnesium and/or manganese ions (By similarity). Inhibited by rolipram and diazepam. Purine metabolism; 3',5'-cyclic AMP degradation; AMP from 3',5'-cyclic AMP: step 1/1. Interacts with LYN (via SH3 domain). Interacts with ARRB2. Additional isoforms seem to exist. Proteolytically cleaved by CASP3. Belongs to the cyclic nucleotide phosphodiesterase family. PDE4 subfamily.