in this pic you can see arnolds fully developed upper and lower pecs studded on a huge rigcage.
IT is important for the beginners to first develop a wide rib cage.This can be achieved by doing pullovers

Instructions

Preparation

Lie upper back perpendicular on bench. Flex hips slightly. Grasp barbell from behind and position over chest with elbows bent slightly.

Execution

With elbows bent slightly, lower bar over and beyond head until upper arm is approximately parallel to torso. Return and repeat.

Comments

Fix elbows 15° to 30° throughout exercise. Keep hips from raising up significantly. Also see Barbell Bent Arm Arm Pullover.