A 34-year-old man presents with dyspnea and increasing peripheral edema. He recently had a "flu like" illness with intermittent sharp left-sided chest pain. On examination, his jugular venous pressure (JVP) is elevated at 8 cm, heart sounds are soft and the blood pressure (BP) is 125/80 mm Hg with a 20 mm Hg decrease in systolic arterial pressure during slow inspiration. Which of the following is the most likely diagnosis?