Auricular fibrillation is a common arrhythmia in adults. According to White, 1 it probably ranks third in order of frequency, premature contractions being first and paroxysmal tachycardia second. In children this form of arrhythmia has been regarded as extremely uncommon, and reports of only a few cases in children under 10 years of age appear in the literature (Price and Mackenzie, 2 Sutherland and Coombs, 3 Ehrenreich, 4 Ogden, 5 Resnik and Scott, 6 Leys and Russell, 7 Sidel and Dorwat, 8 Barber and Middleton, 9 Schwartz and Weis 10 ). The number recorded in patients between the ages of 10 and 17 years is somewhat larger (Barber and Middleton, 9 Schwartz and Weiss, 10 Cookson 11 ). Most of the cases described had their onset in the course of an active rheumatic carditis or were observed in association with inactive rheumatic cardiovalvular disease. The impression is received that the outlook is