This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S., Subject name: Medicine
[{'content': 'A wave in JVP is absent in: \nSelect and explain. \nA. Atrial fibrillation, B. Heart block, C. Tricuspid regurgitation, D. Complete heart block', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) Atrial fibrillationRef: Harrison 19th ed. /1443-1444* A wave in JVP is due to atrial contraction. In atrial fibrillation, since the atria are twitching, the power of atria is reduced to a level that a wave would be absent.* Heart block will have large a waves.* Tricuspid Regurgitation has absent x and large v waves.* Constrictive Pericarditis has a large y descent.', 'role': 'assistant'}]