What does mitral stenosis results in?

Depends on severity. Progressively restricted opening of the mitral valve, measured by serial echocardiography, results in higher pressures in the lung circulation and reduced cardiac output when exercising. Worsening shortness of breath and cardiac arrhythmias may be the result. There are evidence based guidelines to help your doctors decide when to intervene to improve quality and length of life.
Depends. Mitral stenosis restricts the blood flow from the lungs into the left ventricle (main pumping chamber). So the pressure builds in the left atrium and it dilates. The pressure also builds in the lungs. The left ventricle has trouble filling so it pumps less blood to the body. So as stenosis worsens patients develop shortness of breath, funny heart beats, heart failure, high blood press in lungs.