Taussig's early career in pediatric cardiology at Johns Hopkins consisted of studying babies with congenital heart defects and rheumatic fever, an inflammation of the heart and other organs resulting from bacterial infection, which was at the time a major source of child mortality. In the early 20th century, rheumatic heart disease made up the majority of clinical cardiology work: congenital heart defects were considered hopeless curiosities as the surgical means to correct them were extremely undeveloped so relatively little could be done to prevent the early deaths of patients with these conditions.