I read with great interest the study analyzing long-term outcomes after the Fontan procedure in a large single-center cohort.1 The authors provide valuable data from two decades of experience; however, one aspect of potential importance remains unexplored: the striking male predominance (67%) within the sample.

Such a degree of gender imbalance is not typically seen in major international Fontan registries, in which sex distribution is generally more symmetric and seldom surpasses a marginal male predominance.2 This discrepancy prompts an important question: does the observed distribution reflect true biological differences in the epidemiology of single-ventricle physiology, or could it signal gender-based disparities in diagnosis, referral pathways, or access to surgical care?

Growing evidence highlights that sex-related inequities may be present across the congenital heart disease continuum. Several health systems report delayed diagnosis in girls, later referral to tertiary centers, and lower likelihood of early surgical intervention for complex congenital lesions. These differences often arise not from biological prevalence, but from sociocultural, economic, and structural factors, including caregiver perception, healthcare-seeking behavior, prioritization biases, and regional variability in resource allocation. In this context, the absence of discussion regarding the marked male predominance may inadvertently overlook a potential signal of systemic or gender-based access inequality.

Additionally, sex-specific physiological nuances could differentially influence Fontan outcomes. Variations in somatic growth, muscle mass, anemia susceptibility, hormonal transitions, and cardiopulmonary exercise capacity have all been implicated as factors that may shape the long-term trajectory of the Fontan circulation. Without evaluating whether female patients exhibited distinct postoperative courses or differential rates of late complications, has an opportunity to explore clinically relevant interactions between sex and Fontan physiology potentially been missed?3

Given the magnitude of the sex imbalance reported, and considering its possible implications for equity, risk stratification, and long-term prognosis, we believe that the manuscript would be strengthened by incorporating sex-stratified analyses or, at the very least, discussing plausible biological and systemic explanations. Understanding whether this predominance reflects inherent demographic patterns or modifiable disparities is essential not only for interpreting outcomes accurately, but also for advancing equitable congenital heart disease care.