Sounds nasty - basically you need to establish whether you have a partial tear or complete tear of your pec. Generally if you have a severe tear of the pec, then your Wikipedia reference-linkrotator cuff +/- anterior deltoids will kick in hard to stabilise your shoulder if you are holding a heavy object. See a sports physio and see if its partially torn or complete. Complete tears often have a large amount of bruising down your arm or chest wall after 3-7 days ranging from black/blue to yellow in color. If you lie on your back with your hands straigh up in the air and press your palms together and see a large/mishapen bulge or anatomical difference from the other side - this could indicate that you have completely ruptured your pec. You will need this repaired if it is. The rotator cuff is a whole other kettle of fish - best to get it checked out before lifting again to prevent futher damage (best time is about 2-3 days post injury)
Good luck man.