A number of teams are presently working on ways to replace artificial pacemakers with biological solutions: researchers "have now taken preliminary steps toward using a patient's own cells instead of a pacemaker, marking the first time tissue-engineering methods have been used to create electrically conductive tissue for the heart. ... [scientists] obtained skeletal muscle from rats and isolated muscle precursor cells called myoblasts. They 'seeded' the myoblasts onto a flexible scaffolding material made of collagen, creating a 3-dimensional bit of living tissue that could be surgically implanted in the heart. ... When the engineered tissue was implanted into rats, between the right atrium and right ventricle, the implanted cells integrated with the surrounding heart tissue and electrically coupled to neighboring heart cells. ... The implants remained functional through the animals' lifespan (about 3 years)."

Link: http://www.childrenshospital.org/newsroom/Site1339/mainpageS1339P1sublevel223.html