Hi everyone, I've recently been having fainting spells whenever I do cardiovascular exercise. I have been blacking out after the first 10 minutes. My garmin activity tracker records my heart rate as falling to as low as 33 bpm whilst this is happening (It is a wrist-based tracker and I am aware that they aren't the most accurate, but it does usually work quite well). This has only been happening over the last 4 months, since I started on Avonex and I am not sure if it could be related to that. I have been to see my GP who said low blood pressure/fainting is not listed as a side effect for Avonex so it probably isn't that. I didn't think MS would be a likely cause as if it was affecting my heart then it would be a problem the whole time, and not only when I'm exercising, right? I have been referred on to have a 24-hour blood pressure monitor one day this week, and also will be going for an ECG on Monday, so at least my GP is being super thorough! I hadn't mentioned it to my neurologist or MS nurses as I didn't think it was relevant, but will be sure to bring it up when I next see them. Does anyone else have any similar experiences with fainting during exercise?