Here's a drawing to help clarify the above photo.

In this picture you can see that one of the leaflets of the Mitral Valve (interior leaflet) is bulging into the Left Atrium. This bulge is what we call Mitral Valve Prolapse. Each leaflet of the Mitral Valve is connected via Chordea Tendonae to a separate Papillary Muscle. The Papillary Muscles are an extension of the heart wall. When the leaflet of the Mitral Valve bulges it puts tension on the Chordea Tendonae and Papillary Muscle. This will cause pain in the patient. For some people this is very severe pain causing them to cry.

Since one of the leaflets is bulging, the two leaflets are not coapting (not coming in contact with each other). This causes some leaking back through the Mitral Valve and into the Left Atrium (regurgitation).