A 28-year-old pregnant woman develops sudden onset of dyspnea and tachycardia with no other physical findings. Which of the following is the most likely diagnosis?

Sudden onset of unexplained dyspnea is the most common and often the only symptom of pulmonary embolism. Findings on physical examination may be deceptively normal, but tachycardia is a consistent finding. Pleuritic chest pain and hemoptysis suggest a peripheral embolism adjacent to the pleura.