A selective inhibitor of the cGMP-specific phosphodiesterase (PDE2) (IC₅₀s = 0.8 and 2 μM from human and porcine myocardium, respectively, 3.5 μM in rat hepatocyte, and 5.5 μM in human platelet). Also a reversible adenosine deaminase inhibitor (IC₅₀ = 1.2 μM in human red blood cells)