Strep Viridans is a VERY common bacteria in the mouth seen in most gingival and other periodontal disease processes. The worry is when doing a root canal or other dental procedure that the Strep Viridans will get into the blood stream and cause an infection on your heart valves, another place that Strep Viridans seems to grow.

I don't know if the causation has been 100% proven. But the correlations and specific cause of why their would be a correlation are well established. But then again I am just posting on a random internet forum, you should probably talk to your dentist/doctor.