Mitral stenosis primarily restricts the return blood volume to the left ventricle. If the stenosis is particularly severe, it can lead to a significant decrease in return blood volume, resulting in poorer pumping function. There are several main factors that affect return blood volume. The first is sufficient circulating blood volume, and the second is the degree of mitral stenosis. Therefore, after using vasodilators, a large amount of blood flows into the capacitance vessels. As a result, the return blood volume decreases, which can further reduce the return blood volume through the already narrowed mitral valve, leading to worsening breathing difficulties in patients, severe cases can cause fainting, or even sudden death.