A 64 year old man presented with a two year history of exertional dyspnoea, which improved with rest. He reported laboured breathing after walking for about 10 minutes on the flat or after climbing one flight of stairs. He had no chest pain or other symptoms. His medical history included hypertension and pulmonary embolism. He was a retired mechanical engineer with no family history of cardiac disease and was a non-smoker.

On examination, his pulse was 60 beats/min and blood pressure 130/80 mm Hg. His jugular venous pressure was not raised, his heart sounds were normal, and he had no peripheral oedema. Electrocardiography showed sinus rhythm, with low voltage complexes in the limb leads, poor R wave progression, and no evidence of left ventricular hypertrophy. Chest radiography showed clear lung fields and increased cardiothoracic ratio.

Transthoracic echocardiography with harmonic adjustment showed grossly thickened myocardium with a “speckled” appearance, impaired long axis left ventricular function with an ejection fraction of 53%, thickened mitral and tricuspid valve leaflets, and evidence of diastolic impairment. We performed computed tomography to investigate differential diagnoses of breathlessness, including coronary artery disease and chronic pulmonary embolism. Computed tomography showed unobstructive mild calcification of the left anterior descending artery and no evidence of pulmonary embolism. The patient collapsed after being given metoprolol as part of the computed tomography imaging protocol. An electrocardiogram taken after initial resuscitation showed atrial flutter with 3:1 block. Cardiac magnetic resonance imaging confirmed myocardial thickening seen on previous imaging and showed circumferential transmural delayed enhancement of the left ventricle and to a lesser extent the right ventricle.