This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pharmacology
[{'content': 'The biochemical mechanism of action of digitalis is associated with \nSelect and explain. \nA. An increase in conduction from Atrium to ventricle, B. An increase in ATP synthesis, C. An increase in systolic intracellular calcium levels, D. A block of calcium channel', 'role': 'user'}, {'content': "Answer: C \nExplanation: Digitalis medicines strengthen the force of the heabeat by increasing the amount of calcium in the hea's cells. (Calcium stimulates the heabeat.) ... Digitalismedicines control irregular hea rhythms (called arrhythmias) by slowing the signals that sta in the sinoatrial (SA) node. Refer katzung 11e p 214", 'role': 'assistant'}]