I'm one year out of my aeortic valve replacement surgery. I had an artifical mechanical valve put in. I'm a very active (run marathons, triathlons) 22 year old male. I take lisiniprol for high blood pressure. Every once in a while I extreme dizziness. I feel like I'm going to pass out and everything begins to get very blurry. Once I sit down my dizziness goes away after a while. My doctor says it's because I'm dehydrated but I feel like I drink a lot of water everyday and it seems to happen. This only happens about once a month. Does anybody else have problem with this? Is there something wrong with me besides being dehydrated or should I start chugging more water?