Yeah, Clen is the one that can cause cardiac atrophy (enlargement)...but it's rare, and only in high doses (above 1 mg...) ...We're only talking about micrograms (mcg's)...so if you stay under 120mcg/day, you should be fine...You will notice increase anxiety, sweating, maybe shaking, and rapid heart-beat...this is all from the metabolic affects of clen. Again, I would stay away from t3 tho..its much more dangerous long term.
As far as what to stack clen with...from my research, it appears Anavar is the best anabolic to cut fat/gain lean muscle with...you wont see dramatic affects like from some of the bulking gear (dbol, etc), but it's a nice cutting cycle...here's my link to what I think I'll be doing to pre-train for swimming season...(near the bottom)
http://forums.steroid.com/showthread.php?t=419594
ps...benedryl works if you take it at night while on clen, by increasing the amount of time clen will work for. Normally your receptors wont work with clen after a few weeks...but benedryl "up-regulates" the beta-receptors, so that they are available for clen attachment longer...it will just allow you to use clen for 6-8 weeks, instead of 3-6...