A 28-year-old woman recently developed symptoms of chest pain that changed with positioning. It was worse when lying down and relieved when sitting up. The pain is better now but she notices increasing dyspnea and edema. On examination, the blood pressure is 85/60 mm Hg with a positive pulsus paradoxus, low volume pulse at 110/min, and the heart sounds are distant. The JVP is at 7 cm with a negative KussmauTs sign. There are low voltages on the ECG, and a large cardiac silhouette on the CXR.For the above patient with shortness of breath and peripheral edema, select the most likely diagnosis.