LOWN and associates, in 1962, introduced the technique of synchronized direct-current countershock for the reversion of cardiac arrhythmias.1Since that time, a number of papers have appeared attesting to the usefulness of this technique,2,3not only in adults but also in infants.4 This paper presents the case report of a patient with mitral stenosis and atrial fibrillation who underwent successful mitral valvotomy followed by direct current countershock during the fifth month of her pregnancy, with subsequent delivery of a normal full-term infant. Report of a Case A 37-year-old white married woman was admitted to Colorado General Hospital for the first time July 22, 1963, for a mitral commissurotomy. She had had acute rheumatic fever at the age of 13 years and a heart murmur had first been noted at 19 years of age during her first pregnancy. Only mild fatigability was noted during her first three pregnancies.