A 51‐year‐old shop assistant presents to his GP with increasing shortness of breath on exertion. Normally his exercise tolerance when walking is unlimited but more recently he can walk approximately 50 m before having to stop to catch his breath. He also complains of intermittent frontal headaches over the last 2 weeks. On direct questioning, he denies a cough, orthopnoea or haemoptysis. He has not noticed blood in the stool or haematuria. He has never smoked and only drinks occasional alcohol. On examination he had a pulse of 110 beats/min (regular, normal character), BP 115/80 mmHg, pale conjunctivae but no jaundice, and a soft ejection systolic murmur loudest at the aortic area, with no radiation. Abdominal examination was normal.

A full blood count taken 3 years ago showed a haemoglobin of 12.3 g/L with a mean cell volume of 89 fL.

Blood tests showed:

Electrolytes, liver function and inflammatory markers: normal