Abstract Acquired complete atrioventricular block in the pediatric patient is probably less common now than congenital complete atrioventricular block. However, it is not a rare finding. The causes vary from structural to inflammatory and infiltrative abnormalities. Corrected transposition of the great vessels has a 20% to 30% incidence of complete atrioventricular block. This block may develop after birth, and the timing of the development of the heart block varies from individual to individual. Histopathologic findings have detailed an anterior atrioventricular node with a long common bundle, which may be susceptible to ongoing trauma. Post-operative complete atrioventricular block, which at one time had an incidence of 5% to 16% in the early era of corrective surgery for congenital heart disease, now has an incidence of 1% to 4%, depending on the type of surgery. Structural damage from anterior and inferior myocardial infarctions have also been shown to produce heart block, although their occurrence in the childhood population is quite uncommon. Anterior myocardial infarctions appear more likely to produce a permanent complete atrioventricular block compared with an inferior myocardial infarction. Inflammatory or infectious diseases such as myocarditis and Lyme disease have also been associated with acquired heart block in the pediatric patient. This may be either transient or permanent. Rarely, bacterial endocarditis has been associated with complete atrioventricular block. This is generally associated with endocarditis involving the aortic valve. Finally, infiltrative as well as degenerative diseases and traumatic myocardial injury rarely have been found to cause acquired atrioventricular block in childhood.