You're questions are trivial..
First you must realize all the side effects POSSIBLE with anabolic or androgenic steroids...
With those side effects, along with genetics or predisposed heredity, you can seriously injure your organs.
My best answer would be that the kidneys have are your major organs that filter out your waste bi-products...well a lot of steroids can build up nasty bi-products in your system and sometimes "dirty" gear from mexico fucks up your system because not all of your white blood cells can fight against this huge amount of chemicals in your system (that your body has ever seen before)
Therefore your kidneys work overtime in concentrating on trying to filter out everything..its very rough on them..
Also, how much androgen can enlarge teh heart? I dont think its an androgenic question..more so of an anabolic question..Increased size of organs (the heart is a muscle) is due to anabolism not androgenism..So how much anabolic gear will increase your heart size? not sure..but I know HGH can do so (and THAT is self explanatory)
Now does deca or primo enlarge your heart? Nobody knows...it CAN happen but will it? Nobody knows..why not? Well the FDA isnt exactly sponsoring studies on steroid use etc..most of the info on steroid use is from anecdotal reports..
GOod luck bro.