Three weeks after surgery to implant a mechanical aortic valve, a 70-year-old man develops chest pain, fever, and leukocytosis. On examination, the JVP is increased, there is a mechanical S2 sound, and a pericardial friction rub. Which of the following is the most likely diagnosis?

The principal symptom is the pain of acute pericarditis that usually develops 1-4 weeks following the cardiac surgery but could appear after months. It can also occur after myocardial infarction (Dressler's syndrome) or after trauma to the heart (stab wound, blunt trauma). The syndrome can remit and recur for up to 2 years. The acute symptoms usually subside in 1-2 weeks.