This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Which drug directly stimulates contraction of cardiac muscle \nSelect and explain. \nA. Digitalis, B. ACE inhibitors, C. Nesiritide, D. Losaan', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is'a'i.e., DigitalisCardiac glycosides (digitalis) act directly on the hea to increase the force of contraction.", 'role': 'assistant'}]