There is something special about the human heart. We live with, and by, its constant beat. We invest it with our deepest feelings. So naturally we reserve something like reverence for the surgeons who try to fix them when they are broken. Samer Nashef has chosen to write with honesty about the highs, lows and limitations of life and death surgery. He spoke to Hardtalk's Stephen Sackur at the Hay literary festival in Wales.