Left ventricular endomyocardial biopsies were obtained in 19 infants and children using a long sheath as an introducer after transseptal puncture of the atrial septum. From July 1982 to August 1983, 19 patients, ages 7 months to 12 years (mean = 4.6 years), underwent both right and left ventricular biopsies with only one failure. The long sheath technique allows positioning of the bioptome in different areas of the left ventricular chamber. Right ventricular biopsies were also obtained with the long sheath technique in 11 other patients.