Mitral Valve Leaflet Prolapse
The patient's position should be supine.
In this case, a mid-systolic click is immediately followed by a late systolic diamond-shaped murmur that runs to the end of systole. The intensity of the murmur increases and its starting point begins earlier in systole as left ventricular volume decreases (going from supine to standing).
On the anatomy video you can see that the murmur is caused by the prolapse of the posterior mitral valve leaflet. The murmur is represented by turbulent flow from the left ventricle into the left atrium.