Echocardiography of a young man with dyspnoea. Subaortic membrane.

A 19-year-old man presented with a 4-month history of progressively worsening shortness of breath on exertion associated with atypical chest pain. He had a history of heart murmur detected during childhood, but otherwise, he was well. He denied having a previous diagnosis of rheumatic fever. Physical examination revealed a water hammer pulse and a holodiastolic and systolic murmur in the aortic area. A transthoracic echocardiogram showed normal LV systolic function and a pressure gradient within the left ventricular outflow tract (LVOT) (figure 1).Figure 1 Transthoracic echocardiogram apical long-axis view (A); colour flow imaging at the left ventricular outflow tract level (B).Which of the following is the most likely diagnosis? …