Dr Kevin Fong finds out how close scientists are to being able to mend your heart if it stops working. He meets some of the people who have undergone pioneering heart operations and the scientists who are pushing the limits of cardiac treatment. We meet a man who has had his heart replaced with an artificial one powered by a mechanical pump he carries around in a rucksack, and witness a scientist bring a dead animal heart back to life on a workbench. Plus, the work of an American scientist who is using stem cells to turn what she calls a 'ghost heart' - the scaffold of a heart - into a replacement heart for humans.