I can't say for sure, but I've been lead to believe that tachycardia in itself is not a danger. I have a brother with Mitral Valve and have heard all my life that it is also not dangerous or fatal. As for POTS, I'm still learning about my condition, but everything I've read and been told has indicated that POTS is not dangerous or fatal, though I do not know how a rapid heart rate would affect a pregancy. No doctor I've seen yet has ever said anything to me about being careful if I have a baby, or anything like that, and I guess they would've if it were a big concern. If I were you, I'd see an autonomic specialist. They usually fall under the category of cardiology, and they specialize in things like rapid heart rate conditions. As long as your heart is structurally normal (you can find that out by having various heart tests) then you shouldn't really be at risk just because of the tachycardia. I'm going to look into it further as well in the future and will be sure to post any info my doctor gives me!