The mitral valve is on the left side of the heart. It lets blood flow from the upper to the lower heart chamber. Mitral valve regurgitation is diagnosed when the mitral valve in the heart does not close well, which causes blood to leak back from the left ventricle into the left atrium. Mitral valve regurgitation forces the heart to work harder to pump extra blood out of the heart.
Measurement of a track. The proper length for a competitive running track is 400 m (1,312.3 ft). Some tracks are not built to this specification, instead some are legacy to imperial distances like 440 yd (402.3 m). Prior to rule changes in 1979, distances in Imperial units were still used in the United States.
There are running events and field events.   The relays in high school track and field are the 4x800, 4x400, 4x200, and the 4x100.   There are also the 800 dash, 400 dash, 200 dash, and 100 dash. The 300mm hurdles, 100mm hurdles for girls, and 110mm hurdles for guys.