Ondansetron is a medication routinely given to mothers having cesarean deliveries to help prevent and treat nausea and vomiting. The investigators are studying the hemodynamic effects of prophylactic ondansetron on parturients undergoing elective cesarean deliveries under spinal anesthesia.

Spinal anesthesia is a routine anesthetic technique for elective cesarean deliveries. Although this provides safe and effective surgical anesthesia, it is not without side effects, including both hypotension and bradycardia. The incidence of hypotension following spinal anesthesia has been estimated to be as high as 80% in an obstetric population. A number of factors are also likely involved in the development of hypotension and bradycardia, including the Bezold-Jarisch Reflex (BJR).

Two human studies with spinal anesthesia, one in an obstetric population, have demonstrated ondansetron's ability to presumably attenuate the BJR and better prevent hypotension by antagonism of 5-HT3 receptors. Maintenance of blood pressure and heart rate are vitally important, as they are required for adequate perfusion of the fetus prior to delivery.

The investigators plan to investigate the hemodynamic effects of prophylactic ondansetron on parturients undergoing elective cesarean deliveries under spinal anesthesia.

Ondansetron is classified as a Pregnancy Category B drug by the FDA, meaning that no adverse fetal effects have been demonstrated in animal studies, but that there is a lack of well controlled studies in pregnant humans.

Inclusion Criteria:

• Elective CD under spinal anesthesia
• Fluency in English

Exclusion Criteria:

• Contraindication to spinal anesthesiA
• Allergy to ondansetron