mitral valve prolapse
"I was diagnosed with mitral valve prolapse syndrome my senior year in college, resulting in a medical discharge from the Army rather than commissioning as an officer. I was blacking out, fainting, and my activity tolerance dropped dramatically as the condition progressed. 



Metoprolol was prescribed for me to help regulate my heart rate - it worked great for that. I didn't feel the palpitations and heart racing with minimal activity. Downside was that my blood pressure was already low - so being on this medication made my blood pressure drop even lower. Doctors eventually put me on MIDODRINE which constricts my blood vessels causing an increase in blood pressure. The combination works great!"