All newborn infants have limited pulmonary reserve compared with older children. This puts them at increased risk of respiratory complications, such as those associated with infection by the respiratory syncytial virus. Young children with congenital cardiac disease are particularly likely to suffer severe disease related to infection by the virus. In these children, the extreme vulnerability of the lung to pulmonary oedema is compounded by the additional burden caused by the respiratory syncytial virus.

In addition to the well-documented acute pulmonary effects of infection with the respiratory syncytial virus, there may also be consequent long-term respiratory morbidity. Clinical studies have shown that infection by the virus in infancy is associated with a higher risk of developing subsequent bronchial obstructive disease. Much debate surrounds the mechanisms underlying this association. It is thought that a combined immunological and neurogenic response mechanism is likely. Prevention of severe respiratory disease in infants and young children with congenital heart disease due to infection by the virus may, therefore, offer both immediate and long-term benefits. Indeed, an increasing body of evidence supports this hypothesis, indicating a clinical rationale for prophylaxis against the virus in infancy, in order to reduce the chance of developing reactive airways disease and asthma in later life.