Genetic cardiac dysrhythmias, although rare in pediatrics, may be often the first manifestation of the main disease or may determine the vital prognosis in some of these diseases (e. g. Friedreich's ataxia and Duchenne's progressive muscular dystrophy). This is more so, as at present, technical possibilities of implanting pacemakers, at ever smaller ages, are ever so great. The first part of the paper deals with these aspects, reviews, and analyses a large variety of genotypic diseases (metabolism genetic diseases, cardio-skeletal syndromes, neuromuscular diseases, cardio-auditory syndromes, etc.) and also a series of tachydysrhythmias or isolated familial conduction disturbances (blocks). Within each entity, the authors describe the main elements allowing the diagnosis, with special references on the rhythm and cardiac conduction disturbances that may appear, and with the necessary therapeutical considerations. The second part of the material presented is devoted to the cardiac dysrhythmias following the surgical intervention on heart, frequently used at present in the congenital heart diseases, at ever smaller ages due to the special progress in anesthesia and intensive care techniques. Correlation of various types of surgeries with the anatomical lesions of the excitation-conduction system they can involve, makes easier the understanding of the nature and appearance risks of some postsurgical rhythm and cardiac conduction disturbances. The distinction is made between early postsurgical dysrhythmias--that are often episodic--and tardy dysrhythmias that may relapse or become chronic, thus raising difficult treatment problems and sometimes require a secondary pacemaker implantation, given the major handicap they represent for the child.