Grasp two dumbbells. Lie supine on bench. Support dumbbells above upper chest with arms fixed in slightly bent position. Bend elbows slightly and internally rotate shoulders so elbows point out to sides.
Lower dumbbells outward to sides of shoulders. Keep elbows fixed in slightly bent position. When a stretch is felt in chest or shoulders, bring dumbbells back together in hugging motion above upper chest until dumbbells are nearly together. Repeat.
Keep shoulders internally rotated so elbows point downward at bottom position and outward at top position. Shoulder will likely have less range of motion in lower position as compared to Fly on flat bench.