Contributions to the field of congenital heart disease (CHD) by Canadians are well known. Much has been written about Maude E. Abbott of Qu ebec: Prevented from practicing medicine in Montr eal, she took on the task of running McGill University's pathology museum, producing the first atlas of CHD. 1 The description of an absent sinus (inflow tract) of the morphologically right ventricle with a single morphologically double-inlet LV, infundibular outlet chamber with normally related great arteries, the Holmes heart, so named for the first Dean of McGill's Faculty of Medicine, was published by Maude Abbott in 1901 at the recommendation of William Osler. 2,3 The Holmes heart was subsequently imaged with the use of magnetic resonance imaging and used for the cover of the 6th edition of Perloff's Clinical Recognition of Congenital Heart Disease in 2012. 4 Abbott's meticulous recording of both anatomy and first-time documentation of longevity and death makes her possibly the first CHD epidemiologist of the 20th century. Modern techniques in surgical repair, resulting in first-time survival of children born with complete transposition of the great arteries were led in Canada by William T. Mustard at the Hospital for Sick Children in Toronto. Mustard used a pericardial patch to simplify the lifesaving procedure originally described in 1959 by Ake Senning in Stockholm, 5 publishing his results in 1964. 6 To this day, that hospital remains a leading Canadian and international pediatric institution. Emerging from one of the largest pioneering adult-CHD (ACHD) programs in North America, Gary Webb of Toronto, led first-time efforts to establish a regional, provincial, and national care plan for ACHD patients and training of emerging ACHD specialists. Webb launched the first network dedicated to ACHD professionals, the Canadian Adult Congenital Heart (CACH) Network, 7 securing a position as a recognized affiliate of the Canadian Cardiovascular Society in 2010. In an initiative that brought together international leaders in CHD, the first consensus conference on the care of ACHD patients was held in Canada in 1996, with proceedings published in l998. 8 Robust scientific inquiry is new to ACHD compared with other cardiovascular diseases. "Adult congenital heart disease" was coined as a new subspecialty by J.K. Perloff in 1991. 9 The following 10-15 years were dominated by single-centre studies reporting postoperative longevity for up to 200 or 300 patients with increasingly well characterized anatomic substratesdfrom Toronto, the Mayo Clinic, the University of California in Los Angeles, and the Royal Brompton in England. As a field, we began our journey first by marvelling that in patients with repaired atrial septal defect, tetralogy of Fallot, atrioventricular septal defects, and baffle procedures for complete transposition of the great arteries, long-term survival was possible, as reported in single-centre studies with strong surgical teams. 10-14 We soon realized that the road ahead would be marked by emerging complications;...