Is taking msm a bad choice for one that has mitral heart valve problems problems?

Probably. Msm is a sulfur compound sold to people as a supplement. It is not an fda-regulated prescription drug, so it's effects, it's quality, it's consistency, it's benefits, and it's dangers are not well studied and may be unknown. Msm is not proven to help people, and people are not proven to be missing msm. This all means that msm needs more research before it can be considered not "a bad choice".