Transcriptomic analysis of heart tissue from 29 pediatric and 35 adult dilated cardiomyopathy patients revealed dramatically different disease mechanisms, with only 7.4% of differentially expressed genes shared between age groups. Pediatric hearts showed activation of developmental pathways like WNT/β-catenin and Notch signaling, while adult hearts exhibited metabolic dysfunction, mitochondrial deficits, and inflammation. Critically, the β1-adrenergic receptor signaling network remained activated in children but was extensively remodeled in adults, potentially explaining why β-blockers—highly effective in adult heart failure—show limited efficacy in pediatric patients. This finding challenges the current practice of extrapolating adult heart failure treatments to children and suggests pediatric dilated cardiomyopathy represents a fundamentally different disease requiring age-specific therapeutic approaches. The research provides molecular evidence for why guideline-directed medical therapy derived from adult studies has failed to demonstrate mortality benefits in pediatric trials. However, as this is a preprint awaiting peer review, these findings require validation through additional studies before informing clinical practice changes.