The athlete's heart, formally introduced by Henschen and Darling in 1899 through observations of cardiac enlargement in endurance athletes, has evolved from a clinical curiosity to a recognized physiological adaptation. Even before this naming, similar constructs such as the soldier's heart in military recruits and the runner's heart in distance athletes suggested early observations of exercise-associated cardiac remodeling-often pathologized or mischaracterized. Today, this phenomenon is understood as exercise-induced cardiac remodeling, comprising structural, functional, and electrical changes that support the demands of sustained athletic performance. This compendium review examines the full spectrum of exercise-induced cardiac remodeling. We begin by tracing the historical context of how the athlete's heart was discovered and progressively understood. We then explore the morphological and functional adaptations that arise with different exercise modalities, distinguishing between endurance and resistance training effects. The review further investigates the molecular and genetic underpinnings of exercise-induced cardiac remodeling, leveraging data from both human subjects and experimental animal models. We also address the clinical challenges posed by exercise-induced cardiac remodeling, including its phenotypic overlap with cardiomyopathies, such as hypertrophic, dilated, and arrhythmogenic right ventricular cardiomyopathy. These overlaps complicate athlete evaluation and risk stratification, particularly in preparticipation screening and return-to-play decisions. Finally, we explore concerns regarding the long-term effects of high-volume endurance training, including potential maladaptation. Together, this review offers a synthesis of current knowledge and a window into the athlete's heart. By integrating perspectives from history, physiology, molecular biology, and clinical cardiology, we aim to highlight the distinctiveness of this phenotype and why it warrants focused scientific inquiry.
Keywords: athletes; cardiomegaly, exercise-induced; endurance training; exercise; hypertrophy.