Hi, Mitral valve prolapse is not that uncommon, and can have a lot of related conditions - some serious and some not. It can be inherited (genetic) so can run in families. If it is more serious it can lead to regurgitation - where some of the blood exits when the valve does not close properly. More serious conditons can require surgery to repair the valve or replacement of parts of the valve. As a stress test is checking the pumping of the heart it can of course be affected by MVP. But an echocardiogram is the best way to fully check it out.
This link at Mayo gives a good description of MVP:
http://www.mayoclinic.com/health/mitral-valve-regurgitation/MM00714

Cheers, Beefy