4-Despiperidinyl-4-(5-oxopentylamino) Dipyridamole-d16 is the isotope labelled analog of 4-Despiperidinyl-4-(5-oxopentylamino) Dipyridamole (D297205); an impurity of Dipyridamole (D492625) which is a selective inhibitor of phosphodiesterase V (PDE 5), a potent coronary vasodilator drug, an adenosine transport inhibitor, and an inhibitor of platelet aggregation.