Patients with moderate to severe mitral stenosis (calcifiation of the mitral valve generally precipitated by an earlier case of rheumatic fever) experience varying levels of inhibition in their breathing and exercise abilities. But sometimes patients exhibit symptoms that are more severe than the level of stenosis indicated by a regular echocardiogram would warrant. In this study, researchers used cardiopulmonary exercise testing and measured exhaled nitric oxide to try to uncover reasons for the discrepancy. By measuring nitric oxide output both before and after exercise, they found nitric oxide has a significant role in regulating the tone of the patient’s pulmonary cardiovascular system, and thus the pressure within the heart.

So if you have mitral stenosis and you feel worse than your doctor says you should, ask him/her about doing an exercise stress test. You don’t want to submit to open-heart surgery unless it’s absolutely called for–and this may be a way to tell.