The release of the pig genome sequence has resulted in an increase in medical research using these intelligent animals. Stroke research is just one area in which pigs and miniature pigs have generated new insights. Transplanting genetically modified pig cells could hold the key to treating patients with stroke, and indeed other brain disorders, like Parkinson's disease. This process of transplanting genetically modified animal tissues, cells and organs into humans (xenotransplantation) has potential for treating a number of diseases. Pig heart valves have been used for many years to replace diseased or damaged human heart valves.