[tremon]

Hard exertion quickly brings me to a point where I almost faint.

This is a (side-)effect of the beta blockers, I suspect. They actively block your heart from exerting itself, which you would need for sustained physical activity.

Beta-blockers are useful as a protective measure after heart surgery, but you can't build up your physique while on them.

[Itsdijital]

This started before I was prescribed beta blockers. I also take a relatively low dose.