Paediatric heart transplant surgery. Here, the surgeon holds the infant's tiny defective heart, about the size of a walnut. The patient, a boy aged 48 days, was suffering from a life- threatening congenital heart defect. Throughout the operation, the function of the heart & lungs was taken over by a machine, & the boy's body temperature cooled to 15 degrees C. The defective heart was replaced with a donor organ; connections to blood vessels were made using sutures 1/3 the size of a human hair. With the heart in place, body temperature was gradually restored to normal; warm blood flushed into the new heart caused it to begin to beat.