I wonder if that is a common thing after heart surgery. Maybe we are all protecting our hearts after? I've noticed slumping, too, though some of it is breast weight, I think. Anyway, my doc talked with me about it, recently. She told me to stand against a wall making sure my shoulder blades touch it and to tuck in my chin. Now that I am aware of it, I am sitting up better and remembering to do as she said.