A 19 year old man presented to the emergency department with sudden onset shortness of breath and sharp left sided chest pain that was worse on inspiration. He had no history of trauma and had been otherwise well before the onset of these symptoms. However, a year ago he had twice presented to hospital with similar symptoms. He had also undergone surgery on one of his heart valves two years previously but was unclear about the details. The only drug he was taking was warfarin for long term anticoagulation.

The patient was tall, thin, and visibly short of breath but was able to complete full sentences. Closer examination showed a respiratory rate of 22 breaths/min, a non-deviated trachea, and reduced air entry over the left hemithorax with a resonant percussion note throughout. Precordial auscultation showed a soft systolic murmur and mechanical S2, which was loudest over the cardiac apex. The jugular venous pulse was not visibly raised, the patient was normotensive, and pulse oximetry measured his oxygen saturation at 95% on room air.

Twelve lead electrocardiography showed normal sinus rhythm with no other abnormalities. Full blood count, renal function, electrolytes, and clotting were all normal, with an international normalised ratio of 1.1 reflecting poor compliance with warfarin. Chest radiography was performed (fig 1⇓).