A 26-year-old male presents to the emergency department complaining of sudden-onset severe chest pain radiating to the upper back for the past 3 hour. He describes it as a tearing sensation in his back. He denies any fevers or chills but reports an episode of syncope prior to arriving at the hospital. He is in significant pain and is unable to remain still. His past medical history is negative. His blood pressure is 140/50 mmHg in the right arm and 110/50 in the left, with a heart rate of 102 beats per minute. He appears to be tall and thin, with long arms, long thin fingers, and hypermobile joints. His sternum has a concave deformity. Cardiac examination reveals a regular rhythm, an early diastolic murmur at the left upper sternal border, and muffled heart sounds. Breath sounds are equal bilaterally without crackles. His radial pulse on the left is diminished compared to the right. ECG demonstrates nonspecific ST-segment changes. Troponin and CK-MB are within normal ranges. A chest X-ray demonstrates a widened mediastinum (Fig. 9.1).