Reperfusion is essential to prevent further deterioration of ischemic tissue, yet it can paradoxically exacerbate myocardial injury. Ischemia/reperfusion (I/R) injury is particularly relevant in pediatric patients with congenital or acquired heart disease, especially those undergoing cardiac surgery. Cobalt chloride (CoCl₂), an inexpensive compound previously used in humans without documented acute toxicity, has recently been identified as an effective postconditioning agent in adult rat hearts. Given that calcium-handling mechanisms differ between infant and adult myocardium—a key determinant of I/R susceptibility—this study examined whether 0.23 mM CoCl₂ also exerts cardioprotective postconditioning effects in infant rat hearts. Isolated hearts were subjected to global I/R using Langendorff preparation, and functional and structural assessments were performed. Hearts reperfused with CoCl₂, whether throughout the 45-minute reperfusion period or only during the first 5 min, exhibited improved developed tension, along with smaller infarct areas and better-preserved histological features. Under normoxic conditions, CoCl₂ behaved as a reversible negative inotropic agent. These findings support the potential use of CoCl₂ as an economical and clinically relevant cardioprotective strategy for the pediatric population.