Although the cardiovascular, renal, and metabolic effects of ritodrine hydrochloride have been extensively investigated, its effect on shunt and oxygen dynamics have not. To define the effects of ritodrine hydrochloride on these parameters, six pregnant baboons were exposed to both low (1.5 μg/kg/min) and high (5 μg/kg/min) concentrations of the drug and compared with six control animals not exposed. Ritodrine had no effect on arterial or mixed venous oxygen tension, the arteriovenous oxygen content difference, or the venous-arterial shunt fractiin. The treated animals did manifest a significant decline in both arterial (p < 0.05) and mixed venous carbon dioxide (p < 0.01) pressures, with associated increases in the respective pH values (p < 0.001 and p <0.01). Total pulmonary resistance also showed a significant fall during ritodrine treatment (p < 0.05). These data support a minimal, if any, impact of ritodrine hydrochloride on the blunting of normal hypoxic pulmonary vasoconstriction. Furthermore, these data are of potential use as a reference in the treatment of pregnant women who have sustained life-threatening insults from exposure to these agents. © 1988.