In mitral regurgitation the valve does not close properly. This causes blood to leak back (regurgitate) into the left atrium when the left ventricle contracts. Basically, the more open the valve remains, the more blood regurgitates, the more severe the problem.Mitral regurgitation can occur if the valve is weakened or damaged.n mitral regurgitation the valve does not close properly. This causes blood to leak back (regurgitate) into the left atrium when the left ventricle contracts. Basically, the more open the valve remains, the more blood regurgitates, the more severe the problem.