Oxytocin antagonists are used as tocolytics in preterm labor. Which among the following is an oxytocin antagonist?

Atosiban is a selective oxytocin vasopressin receptor antagonist capable of inhibiting oxytocin induced myometrial contractions. The mechanism appears to be competitive inhibition of oxytocin receptors in the myometrium and decidua. Oxytocin antagonists result in a decrease in intracellular free calcium that results in decreased myometrial contractility. Ref: Management of High-Risk Pregnancy: A Practical Approach By S. S. Trivedi, Manju Puri, M.D., 2011, Page 91; Danfoh's Obstetrics and Gynecology, 10th Edition, Page 175-178.