Calcium entry blocking drugs may have a role in the treatment of maternal and fetal tachyarrhythmias, as well as for treatment of premature labor. This study was undertaken to assess the hemodynamic effects of verapamil in the awake pregnant ewe. Verapamil, 0.2 mg/kg administered intravenously over 3 min, resulted in the following maternal cardiovascular changes: transient (2 min) but significant decreases in systolic, diastolic, and mean blood pressures, and significant but equally transient increases in central venous pressure and mean pulmonary arterial pressure. Pulmonary capillary wedge pressure increased for 5 min. These results are consistent with the negative inotropic and peripheral vasodilating effects of verapamil. Cardiac output, systemic vascular resistance, and pulmonary vascular resistance were unaffected. Uterine blood flow decreased 25% at 2 min and remained significantly (7-18%) below control levels for 30 min after drug injection. The effects of verapamil on uterine blood flow suggest that it should be used with caution in cases where uteroplacental perfusion is compromised.