A 48-yeаr-оld wоmаn cаlls 911 and is brоught to the emergency room complaining of a sudden onset of dyspnea. She reports she was standing in the kitchen making dinner, when she suddenly felt as if she could not get enough air, her heart started racing, she became lightheaded and felt as if she would faint. She denied chest pain or cough. Her medical history is significant for gallstones, for which she underwent a cholecystectomy 2 weeks ago. The procedure was complicated by a wound infection, requiring her to stay in the hospital for 8 days. She takes no medications regularly, only acetaminophen as needed for pain at her abdominal incision site. On examination, she is tachypneic with a respiratory rate of 28 breaths per minute, oxygen saturation is 84% on room air, heart rate 124, and blood pressure 118/89 mm Hg. She appears uncomfortable, diaphoretic, and frightened. Her oral mucosa is slightly cyanotic, her jugular venous pressure is elevated, and her chest is clear to auscultation. Her apical heart rhythm is tachycardic but regular rhythm with a loud S2 in the pulmonic area, no gallop or murmur. Her abdominal examination is benign. Incision site is normal without signs of infection. Her right leg is moderately swollen from mid-thigh to her feet, and her thigh and calf are mildly tender to palpation. Laboratory studies including cardiac enzymes are normal, her electrocardiogram (ECG) reveals sinus tachycardia, and her chest X-ray is interpreted as normal. What is the most likely diagnosis?