Hapax/medical science

The human heart has four chambers, but only the left ventricle is responsible for building the pressure that moves blood around the body. Depending on one chamber to do the hard work places this part of an artificial heart under enormous strain.

Dr Guha likens the process to trying to scale a four-foot rise in just one bound. "Do it too often and your knees will give way," he said. "Much better to use a series of small steps."

The sudden build-up of pressure inside conventional artificial hearts can also damage blood cells, Dr Guha said. This can lead to clotting and strokes, and means that patients must be given anti-coagulants, which place them at risk of severe bleeding.

By contrast, his prosthetic heart builds pressure in stages, through five chambers -- a model based on the anatomy of a cockroach.