Transvenous (TV) pacing and defibrillation leads are frequently implanted in children as part of treatment for various congenital and acquired rhythm abnormalities. However, the lead-vascular endothelial interaction is not a benign process and is associated with a risk of progressive venous obstruction. Often, this obstruction requires surgical or interventional relief. The risk of obstruction is related to venous diameters at implant and lead size. Since venous diameters are largely unknown at different ages, the purpose of this study was to correlate innominate vein (INN) and superior vena cava (SVC) diameters with body dimensions in growing children.