clen is active in your system for alot longer than the ECA is , if the clen already has your heart rate up and is having a effect on your body then why would you rsik adding somthing else that does the same thing?? sounds like a good recipe for a bad reaction.
its pretty commone to cycle the celn for 2-3 weeks on then take a week or two off and during the off time you use the ECA stack to have the samne effect.
I guess that if yu kept the doses low that you could run them together but i don't see a reason why , they don't have any added benifit of working together