Rheumatic heart disease remains the most important cause of acquired heart disease in children and young adults. Different kinds of rhythm and conduction disturbances may be seen during the course of acute rheumatic fever (ARF). Long PR intervals are found commonly in rheumatic fever, but complete atrioventricular (AV) block is an exceptionally rare manifestation. This case report is about a 14 year-old-female patient diagnosed as ARF based on migratory arthralgia and mild carditis who also developed complete heart block on admission. Electrocardiogram on the 3rd day of hospitalization depicts 2nd degree atrioventricular block (Mobitz I) combined with PR prolongation. The ECG revealed a normal sinus rhythm with PR prolongation on the 4th day of hospitalization. Rarely, complete AV heart block can occur as a complication of ARF and may develop during the acute phase.