Ms TS

Would it be detrimental to my heart if I used a micro-current machine on my face for facial muscle toning and exercise?  The currents used are in the micro amp range and, according to the beauty clinic compatiblel with one's own body electric impulses

I have a very minor mitral valve prolapse and my ECG's show a left bundle branch block.

[Cleveland Clinic]

As long as you don't have a pacemaker and are not going to use this machine over your heart you should be ok.  If you experience any palpitatons or irregular heart rates during the treatment then you should probably stop.  make sure that this device is something that is commonly used, or has been used before by others safely.