Lie supine on a bench with a dumbbell in each hand and the arms straight up with palms facing each other. Lower the dumbbells to the side, keeping the arms close to straight and approximately perpendicular to the body, lowering until you feel a stretch in the pecs but avoiding any pain. Bring the dumbbells back together at the top.
 
Purpose
The dumbbell pec fly is a simple exercise to isolate the pecs to get additional work for them without further work for the delts or triceps, or to pre-fatigue the pecs for bench or dip variations.
 
Programming
Generally higher reps like 12-20 reps are appropriate. Heavy weights are discouraged because of the precarious position at the bottom.