The design, synthesis, and pharmacology of a new class of compounds possessing both thromboxane receptor antagonist and thromboxane synthase inhibitory properties are described. Replacement of the phenol group of the known thromboxane antagonist series 4(Z)-6-[(4RS,5SR)-4-(2-hydroxyphenyl)-1,3-dioxan-5-yl] hex-4-enoic acid by a 3-pyridyl group led to a series of compounds, 5, which were potent thromboxane synthase inhibitors and weak thromboxane antagonists. Further modifications at the dioxane C2 position led to compounds, 7, which were potent dual-acting agents. In the case of compound 7w, the dual activity was shown to reside almost exclusively in the (-)-enantiomer, 7x. Following oral dosing to rats and dogs, 7x (3 mg/kg) displayed significant dual activity over a period of at least 8 h.