What is mitral valve sclerosis without stenosis and can it be the cause of my shortness of breath with exertion and chest tightness?

Yes. Sclerosis is a hardening, in this case a hardening of the mitral valves. These valves are basically skin flaps that separate the left chambers of the heart. Sclerosis prevents the valves from operating freely and can lead to backflow of blood in the heart. Simply put, your heart will not operate efficiently when under stress. .