Writing Committee consisted of acknowledged experts in hypertrophic cardiomyopathy (HCM) representing the American College of Cardiology Foundation and the European Society of Cardiology. Both the academic and private practice sectors were represented. The document was reviewed by 2 official reviewers nominated by the ACCF, 3 official reviewers nominated by the ESC, 12 members of the ACCF Clinical Electrophysiology Committee, and 4 additional content reviewers nominated by the Writing Committee. The document was approved for publication by the ACCF Board of Trustees in August 2003 and the Board of ESC in July 2003. This document will be considered current until the Task Force on Clinical Expert Consensus Documents revises or withdraws it from distribution. In addition to the references cited as part of this document, a comprehensive bibliography including relevant, supplementary references is available on the ACCF and ESC websites.