A 47-year-old woman is seen with a 1-wk history of progressive shoness of breath, increasing pedal edema, weight loss, and low-grade fever. She has a 40-pack-year smoking history. Physical examination: pulse 138 bpm; respirations 34/min; blood pressure 100/88 mm Hg with pulsus paradoxus of 22 mm. Peinent findings: increased jugular venous distension, normal sinus rhythm with distant hea sounds, and an apex beat that is difficult to palpate. Chest x-ray is shown below.What is the most likely diagnosis?

This PA view shows a large cardiac silhouette with a "water bottle hea." The pulmonary vasculature and the vascular pedicle appear normal. Large cardiac silhouettes are seen in cardiomegaly and are usually associated with signs of pulmonary venous congestion. In this case, the cardiac silhouette is increased due to pericardial effusion. The presence of pulsus paradoxus with distant hea sounds suggests cardiac tamponade secondary topericardial effusion as seen on the chest x-ray. The associated finding would be a low voltage on ECG due to an effusion. Pulsus alternans may also be seen. The Kussmaul sign is seen with constrictive pericarditis. Left ventricular hyperophy and pulmonary edema suggest left ventricular failure. This is not necessarily associated with cardiac tamponade and pericardial disease.