I am having mild mvp with mild regurgitation. Now am having brown vertical line under my nail. Is it due to endocarditis?

Local More Common. Nail bed injuries/hemorrhages are usually from local injuries, rarely endocarditis in which people routinely have chronic (a) low grade fever, (b) splinter hemorrhages visible in multiple nail beds, hands & feet & (c) do not feel well, e.G like "flu". The key to symptom clues, as a part of diagnoses, is integrated patterns & severity of symptoms combined with additional data, eg. Vegetations echo.
Possibly. Splinter hemorrhages can be a sign of endocarditis. Usually there will be other signs and symptoms present, and the more signs we see, the greater our suspicion. If all you have is those hemorrhages, i would be less suspicious, but it's certainly possible, and would have to be considered. I would discuss it with your pcp.