Paediatricsmiddle twist
A 15-year-old boy attends for clearance to play first-grade school football. He has never had chest pain or blackouts and keeps up with the fittest boys at training. His blood pressure is 118/70 mmHg and the femoral pulses are easily felt. His arm span equals his height and the palate is normally arched. There is a grade 2 systolic murmur at the left sternal edge that becomes louder when he stands up from squatting and softer while he grips your hand hard. Which one of the following investigations will best demonstrate the cause of this murmur?