Paediatric heart transplant surgery. This close- up shows the tiny defective heart, the size of a walnut, held next to the transplanted heart. The patient, a boy aged 48 days, was suffering from a potentially fatal 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.