Running the risk: extreme right ventricular remodelling in an endurance athlete-a case report.

Background: Distinguishing physiological cardiac adaptation from pathological remodelling in endurance athletes is challenging. While the athletic heart typically demonstrates balanced biventricular enlargement, extreme exercise may rarely trigger disproportionate right ventricular (RV) changes that challenge diagnostic classification. Case summary: A 47-year-old male ultra-endurance athlete presented with exertional symptoms 3 months after recovery from a pulmonary embolism (PE). Initial post-PE echocardiography was normal. After resuming extreme training, he developed severe RV dilation (basal diameter 5.7 cm on echocardiography; RV volume index 92 cc/m² on cardiac magnetic resonance imaging) disproportionate to the left ventricle, with preserved systolic function and no late gadolinium enhancement. Cardiopulmonary exercise testing revealed significant chronotropic incompetence with below-expected peak oxygen uptake for his elite training status. Symptoms and ventricular ectopy improved with detraining, but severe RV dilation persisted. Evaluation excluded arrhythmogenic cardiomyopathy and significant pulmonary vascular sequelae. Discussion: This case illustrates disproportionate RV remodelling precipitated by the resumption of extreme exercise in a susceptible athlete post-PE. The temporal dissociation from the PE and absence of residual clot burden implicate exercise-related haemodynamic stress as the primary driver, challenging the boundary between physiological adaptation and maladaptation. These findings highlight a potential maladaptive response to extreme exercise, possibly potentiated by a prior vascular insult, and underscore the value of integrated functional assessment and monitored detraining in athletes with borderline findings.