Amid the beeping of heart monitors, a more gentle noise can be heard on the wards of Great Ormond Street Hospital.
The soft voice of music therapist Nick Pickett and the strumming of his guitar are entertaining the young patients in Bear Ward. All the children here are under three years old. Some are facing the long wait for a heart transplant and are being kept alive by the rhythmic beating of a mechanical heart. Sam Wallace's bed is surrounded by balloons, toys and other reminders of home. His grandmother, Viv Green, says the music has a transformative effect.
"Oh, Sammy loves music, he has always loved music."It just makes him happy. He will sing and dance. He loves to dance, he moves with the music as soon as he hears it and it just brightens him up completely - he's a different boy."