Dr. Leland Siwek attended college and medical school at Harvard University. His general surgery residency was at Howard's Massachusetts General Hospital in Boston, Massachusetts. A two-year cardiac surgical research fellowship, focusing on congenital heart disease was completed at the National Institutes of Health in Bethesda, Maryland.

Dr. Siwek's cardiothoracic surgery fellowship was completed at the Massachusetts General Hospital and included a position as Senior Registrar at the Wessex Regional Cardiothoracic Center in Southampton, England. Additional specialty training in congenital heart surgery was obtained at the Boston Children's Hospital as Chief Resident in 1987. Dr. Siwek joined the staff of Sacred Heart and Deaconess Medical Centers in 1988.

He was particularly involved in moving Spokane into the forefront of early complete repair of complex congenital heart defects in young infants and newborns. Several complex newborn operations such as the Arterial Switch operation were just introduced in the Northwest by Drs. Siwek and Leonard. Dr. Siwek's interests continue to include early complete repair of complex congenital heart defects as well as minimally invasive repair of more "simple" defects.