Tropical regions, particularly those with high levels of endemism such as South America, harbor a diverse array of amphibian species. However, these regions often lack specific regulations governing the release of emerging contaminants, including the surfactant nonylphenol ethoxylate (NPE), into water bodies, which can have devastating consequences for these sensitive ecosystems. This study evaluated the sublethal effects of 16-day subchronic exposure to NPE at an environmentally relevant concentration of 30 µg/L on American bullfrog (Lithobates catesbeianus) tadpoles using multiple endpoints, including biometric parameters, antioxidant responses, oxidative stress biomarkers, heart rate, and myocardial contractility. Our results revealed that exposure to NPE elicited a range of harmful effects on tadpoles, including significant reductions in hepatic and ventricular mass, disruptions in antioxidant defenses leading to oxidative stress-mediated damage in cardiac, hepatic, and muscular tissues, and changes in heart function such as negative inotropism and lusitropism, and tachycardia. These sublethal effects could have significant ecological impacts, affecting not only immediate survival but also compromising overall fitness through the reallocation of energy reserves.