The material contained in this book was presented at the Boerhaave Course which was held in Leiden, The Netherlands, on May 2 and 3, 1977. It deals with three topics of considerably recent interest, not only to cardiologists and cardiovascular surgeons, but also to embryologists, anatomists and pathologists. Papers on the development and the normal anatomy of the conduction system include a discussion of the continuing controversy as to whether dis­ crete and anatomically distinct internodal pathways exist in the human heart. These are followed by descriptions of the abnormal anatomy and relation­ ships of the conduction system in certain complex cardiovascular anomalies. The rather startling discovery that there may be a second, ectopically located and functioning atrioventricular node and common bundle in addition to the usual, but non-functioning one has been of enormous importance in the surgical treatment of certain forms of congenital heart disease. The panel presentations comprising the first four papers on the topic of transposition of the great arteries highlight the widely differing views atld the continuing controversies concerning the nature and pathogenesis of this rela­ tively common and important anomaly. Descriptions of the special morpho­ logic features of ventricular septal defect and pulmonary stenosis as they occur in association with transposition are followed by discussions concern­ ing recent advances in the surgical treatment of transposition, and the com­ mon and often troublesome postoperative arrhythmias.