The decline dumbbell flye is an isolation exercise for the chest. The decline angle puts more emphasis on the lower portion of the chest.
Grab a pair of dumbbells and lie face up on an decline bench. Lift the dumbbells above chest, your palms facing each other. Slightly bend elbows.
Slowly lower the dumbbells in an arc down and away from your body. Once the dumbbells are almost in line with chest, reverse the movement back to the starting position. Squeeze the chest muscles at the top of the movement.
Make sure you keep a slight bend in the elbows throughout the movement.
Do not overload the weight. Ease your way into learning the exercise.
Make sure you try to feel the chest muscles doing most of the work.