This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abnormal labor, Subject name: Gynaecology & Obstetrics
[{'content': 'Best tocolytic in a cardiac patient is \nSelect and explain. \nA. Atosbian, B. Isoxsuprine, C. Nifedipine, D. MgSO4', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Atosiban is oxytocin antagonist and best tocolytic in cardiac patients. B agonists and Calcium channel blockers are contraindicated in hea disease complicated pregnancies.', 'role': 'assistant'}]