Nitroprusside (NTP) infusion may result in significant drop in blood pressure, heart attack, rhythm disturbances and stroke. The risks associated with phenylephrine (PE) infusion include blood pressure elevation, heart attack, rhythm disturbances and stroke. The likelihood of this is very small since the medications will be given in small, gradual doses with close monitoring by study personnel and physicians. If significant blood pressure changes occur, the medication will be stopped immediately. Stopping the medication will quickly reverse any blood pressure changes since the drugs have a very short half-life.