Myocardial antibodies are detected by an indirect immunofluorescent technique. Monkey heart tissue substrate is incubated with patient's serum. Antibodies specific for cardiac muscle antigens bind to the tissue and are detected by fluorescein-labeled antihuman immunoglobulin antiserum.(Twomey SL, Bernett GE: Immunofluorescence method for detecting anti-myocardial antibodies, and its use in diagnosing heart disease. Clin Chem 1975;21:1903-1906). All patient specimens are initially screened at 1:20 and 1:40 dilutions.