Profound first-degree atrioventricular block. A 30-year study.

We report the findings in a 60-year-old patient with a 30-year history of profound first-degree heart block with no associated cardiac abnormalities. The sinus node and the His-Purkinje system were normal. The time for atrioventricular nodal conduction was prolonged, with normal refractoriness both before and after administration of atropine, suggesting that the atrioventricular node may be lengthened, although electrically normal.