Exercise-induced cardiac remodelling (EICR) refers to the cardiac structural and functional adaptations that occur in response to the hemodynamic stress of strenuous exercise. Differentiating physiological cardiac hypertrophy as a result of EICR from structural cardiac pathology may be challenging in clinical practice because of the phenotypic crossover between extreme forms of the "hearts of athletes" and mild forms of cardiomyopathy. This structural phenotypic overlap equates to a grey zone of clinical uncertainty. Specifically, asymptomatic athletes presenting with extreme left ventricular (LV) dilatation, LV wall thickening, or right ventricular (RV) dilatation require a systematic and integrative diagnostic approach to achieve accurate clinical differentiation. The combination of a careful clinical history and examination, appropriately used multimodality cardiac imaging, functional exercise testing, ambulatory rhythm monitoring, and occasional detraining typically provides the necessary data for diagnostic purposes and sports participation recommendations. Further clinical distinction of the hearts of athletes from cardiac pathology may emerge from future clinical and translational research efforts establishing exercise-related biomarker profiles and mechanisms underlying EICR adaptations.