A 58-year-old woman with no relevant medical history presented to the emergency department with syncope. Following a long flight 6 weeks prior, she had developed left calf tightness and pain, followed by shortness of breath for 1 week and then a syncopal event the day of admission. On physical examination, she appeared anxious, with a temperature of 36.8°C, a heart rate of 102 beats/minute, blood pressure of 128/66 mm Hg, a respiratory rate of 20 breaths/minute, and pulse oximetry of 98% on room air. Her heart and lung sounds were normal. Her laboratory results were notable for a troponin level of 0.07 ng/mL (to convert to μg/L, multiply by 1.0), and a fibrin D-dimer level of more than 2000 μg/mL (to convert nmol/L, multiply by 5.476). Her electrocardiogram on presentation showed sinus tachycardia and was otherwise normal. Computed tomography of the chest was performed, which showed multiple large bilateral pulmonary emboli (Figure, A), with deviation of the interventricular septum toward the left ventricle. Echocardiography demonstrated a large mobile thrombus extending from the right atrium into the right ventricle, as well as a clot in the left atrium and left ventricle that appeared to originate from the interatrial septum, suggesting a defect there (Video, Figure, B).