SummaryA 1 to 30 year follow‐up study of 54 infants and children with paroxysmal supraventricular tachycardia is presented. In 28 cases the first attack occurred in infancy, and in 18 of these already in the first months of life. Nine patients had organic heart disease. The WPW syndrome was diagnosed in 30 cases. When first seen, most of the infants presented signs of incipient or manifest congestive heart failure, which was very unusual in the children, most of whom had only minor symptoms. Four children had experienced brief syncopes during attacks. Digitalis was effective against congestive heart failure and, when continued, may have prevented failure during subsequent attacks. Whether digitalis and other anti‐arrhythmic agents facilitated conversion to sinus rhythm could not be established in this study. Vagal stimulation was only rarely effective. Preventive treatment with digitalis or other antiarrhythmic drugs seemed to have little if any effect on the frequency of recurrent attacks. Out of 23 infants who were followed for at least 5 years, 17 had been free from attacks during the last 3 years and 13 of these had had their last attack before the age of 6 months. Out of 23 children followed for 5 years or more, only 3 had been free from recurrences during the last 3 years. Patients with the WPW‐syndrome had a somewhat higher incidence of recurrent attacks.