Pec Deck Butterflies are for mid chest muscles / pecs. Pec deck butterflies are an essential part of lifting weights and strength training. You need to go to gym or buy a pec deck machine. It is expensive. Any way on how to do / perform / execute this exercise you have to sit on the pec deck with your back flat on the machine, now squeeze your forearms and elbows in together as if touching each other and go back to initial position.

Video Demos on How to do Peck Deck Butterflyes