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 channels', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Digoxin is a cardiac glycoside. It directly inhibits Na-K ATPase and increases intracellular Na and decrease the extrusion of calcium. Thus increases intracellular Calcium. By increasing the calcium content and sodium content, force of contraction increases. (Ref-Essential of medical pharmacology K D TRIPATHI 6 Edition)', 'role': 'assistant'}]