In the past, pulmonary arterial (PA) structure has been extensively investigated with the aim of providing an insight into operative indication for patients with congenital heart disease (CHD). Although PA histological analysis is applied less frequently in the current era, demographic changes of CHD patients require a refocussing of attention. With an exponential increase in the number of adult CHD patients, it is important to realise how structural changes evolve long after previous procedures as a certain proportion of such cases necessitate surgical or interventional manipulation on their PAs. Herein we present our findings on main PA tissues obtained from a 35-year-old woman who had been palliated with a classic Fontan operation 23 years earlier. Immunohistological analysis showed severe alterations, especially in the medial layer; not only attenuation of muscular component but also disarray and fragmentation of elastic fibres were remarkable, which should represent the adaptive response to longstanding diminished lung perfusion. To our knowledge, these observations have not been well described in the literature, presumably because previous studies were conducted primarily with respect to 'increased' pulmonary flow, and hence little is known regarding structural alterations in response to 'decreased' perfusion. Our findings are provided with a review of the literature.