Prosthetics are mechanical or electrical devices inserted onto or into the body to replace or supplement the function of defective or diseased organs. Artificial limbs designed for persons with amputations were among the first prosthetics; but metal or plastic joint replacements or bone fixations for subjects with severe arthritis, fracture, or deformity are now also available. Replacement teeth for those lost by caries or trauma are included in prosthodontics. Heart valves may failure as a result of rheumatic or congenital heart disease or bacterial endocarditis, and may need replacement with mechanical valves. sutured in place of the diseased valves under cardiorespiratory bypass. If the pacemaker of the heart fails, then an artificial pacemaker can be substituted to stimulate the heart muscle at a set rate.