The new generation of pacemakers satisfy three basic requirements; histocompatibility, small size, and long life. Resins have been abandoned in favour of titanium cases. These are completely sealed and there is no risk of infiltration or histotoxicity. In addition, the employment of low consumption circuits and new sources of energy, especially lithium, has enabled the working life of a pacemaker to be extended virtually to its useful limits. The application of electrical stimulation to the treatment of arrhythmia has led to the creation of automatic or magnetically controlled pacemakers that come into action with pulse volleys on the appearance of otherwise intractable rhythm disturbances.