I have to question if it was related.
It is, if you taking that load what are you talking about... gram or more per day, wow! I am 20, having two years experience with meph, mostly on party, sometimes at home when listen music, and on party I do about 1 gram, home just about a few lines.. Point is, meph or all these stimulants do heart arrhytmia, when your heart is beating and suddenly heart beats faster, after that is compensation break (1-2 seconds), to return to a normal rhytm. "This" is not generally dangerous, cause some people have arrhytmia in normal state (healthy,without drugs) and they live normally. If you do lot of mephedrone, and together you do something that your heart makes pumps faster (runing, go fast up the stairs, or alcohol,..) your heart is confused and harebrained. Cocain is proven toxic for heart muscle, no doubt about it, but meph not, or I think probably not (I study biology and chemistry).. BUT.. makes your heart as I said confused and overloaded.. Few grams with range and with calm or not doing craps is "generally" safe.. Do an alcohol with some coke together with meph, and your heart is in dangerous. RIP your friend, but probably he wasn't 100% healthy if we talking about heart, or just he did looot of stuf.
And guys, you can laugh on me, but I still don't know what is "pre-ban". Something that you take before party to start up, or it means meph when it was legal, or.. ? Yes, I searched 100x times but without result.
Stay safe