When most people think of disease-treating stem cells, they think of a transplant of stem cells. Embryonic stem cells are first specialized in the required type of adult cell in a stem cell transplant. These mature cells then replace tissue damaged by illness or injury. This type of treatment could be used to replace neurons damaged by spinal cord injury, stroke, Alzheimer's disease, Parkinson's disease or other neurological problems; produce insulin that can treat people with diabetes and heart muscle cells that can repair damage after a heart attack or replace virtually any tissue or organ that is injured or diseased. However, much more can be done by embryonic stem cell therapies. Studying how stem cells develop into heart muscle cells could provide clues as to how after a heart attack we could induce heart muscle to repair itself. The cells for toxic side effects could be used to study disease, identify new drugs, or screen drugs. Without transplanting a single ce...