<s>[INST] context: Calcium-channel blockers, especially nifedipine, are safer and more effective tocolytic agents than are B-agonists Nifedipine is the best first-line tocolytic agent available at this time. The initial dose should be 30 mg and subsequent doses 20 mg every 6 hours. MgSO4 which is an excellent drug for ecclampsia prevention and management is also used for tocollyis. This has a'Neuroprotective effect' on the preterm fetus and prevent s cerebral palsy instances main subjective maternal complaints to Mgs04 are related to the mental effects ("out of it" or "felt like a zombie") and the overall muscular weakness produced by the drug. The most frequent side effects of magnesium sulfate are pulmonary congestion, respiratory depression,hypothermia, and neuromuscular toxicity. Infants of mothers treated with IV magnesium sulfate sholy before delivery are frequently Hypotonic . neonatal/fetal complications are hypocalcemia & Intraventricular hage NOTE: FDA had denied approval of Atosiban (Oxytocin receptor antagonist) in view of concerns regarding efficacy and fetal-newborn safety. [/INST] question: Tocolytic of choice in pregnancy with hea disease (OBG) | options: A: Nifedipine B: MgSO4 C: Atosiban D: Alcohol | answer: A </s>