Cyclic nucleotide phosphodiesterase with a dual specificity for the second messengers cAMP and cGMP, which are key regulators of many important physiological processes (PubMed:15260978, PubMed:8855339, PubMed:9419816). Has a preference for cGMP as a substrate (PubMed:9419816). {ECO:0000269|PubMed:15260978, ECO:0000269|PubMed:8855339, ECO:0000269|PubMed:9419816}. This is the function of PDE1B (phosphodiesterase 1B, ENSG00000123360).