We identified a variant in PDE3A (Phosphodiesterase 3A), encoding phosphodiesterase 3A, which was associated with flow-mediated dilatation in adolescents (9–12 years of age; β[SE], 0.38 [0.070]; P=3.8×10−8) and confers risk of ischemic stroke (odds ratio, 1.04 [95% CI, 1.02–1.06]; P=5.2×10−6). This evidence concerns the gene PDE3A and ischemic stroke.