This exercise is great for developing the chest and tricep muscles.
As you move into the fly movement, turn your hands so palms are facing out, this will give you a better stretch through the pec.
As you bring the dumbbells back to the starting position, rotate your palms back so they are facing each other.
From this position, you will keep dumbbells together and lower them towards your chest, push the dumbbells back up by extending your arms straight and contracting pecs and triceps.
Click the link to check out the exercise: Floor Fly with Hex Press