Ive had a pacemaker difibulator implanted in me since i was 25.
The wires are snaked through my lungs and into the heart.
My Docs were worried about impact to that area.
I do Kenpo, and lift.
No problems with lifting, but i shouldnt punch so hard with the left, and i have to cushion my falls more on the left side during takedowns.
The danger is that the wire will rupture stuff on the inside.
I think the Doc is more concern with impact/trauma than lifting with concern to internal ruptures.
Id the Doc to specify the reason for the caution about lifting on the left side.
No cardiologist reccomends lifting, so this reccomendation may be for another reason.