A 64-year-old presents with dyspnea and edema. He had previous coronary bypass surgery 5 years ago, which was uncomplicated. Since then he has had no further chest pain. On examination, his JVP is at 8 cm, with prominent Kussmaul's sign. The heart sounds are easily heard but there is an early diastolic filling sound (pericardial knock).For the above patient with shortness of breath and peripheral edema, select the most likely diagnosis.