A new iridoid was isolated from the Tabebuia avellanedae, its anti-myocardial injury activity was determined, and its mechanisms underlying inhibition of inflammation, regulation of oxidative stress and inhibition of apoptosis were explored. The dried inner bark of the Tabebuia avellanedae was extracted with boiling water, separated by liquid-liquid extraction, and purified by silica gel/ODS/Sephadex LH-20 column chromatography coupled with high-performance liquid chromatography (HPLC) to obtain avelladoid Ⅰ (Avd Ⅰ). The structure of Avd Ⅰ was identified by nuclear magnetic resonance spectroscopy (NMR) and high-resolution mass spectrometry (HRMS). Cardiomyocyte injury model was established by 1 μg·mL^-1 doxorubicin. After treatment with 1-40 μmol·L^-1 of Avd Ⅰ, the cell viability was evaluated by methyl thiazole tetrazolium (MTT) assay, and the lactate dehydrogenase (LDH) was measured. The inflammatory factor levels of interleukin-6 (IL-6), interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) as well as the oxidative stress levels of lactate dehydrogenase (LDH), superoxide dismutase (SOD), malondialdehyde (MDA) and glutathione peroxidase (GSH-Px) were detected. DCFH-DA staining was employed to observe the level of reactive oxygen species (ROS), AnnexinV-FITC/PI double stainings were performed to detect the apoptosis level, JC-1 single staining was used to measure the mitochondrial membrane potential level, and the Incell-Western assay was conducted to determine the apoptosis-related protein expression levels. The results showed that the cardiomyocyte injury was improved by 1-20 μmol·L^-1 of Avd Ⅰ, and the IL-6 and IL-1β levels were decreased to near normal cell levels by 1 μmol·L^-1 Avd Ⅰ. The ROS level was strongly reduced and the SOD level was highly increased by 1 μmol·L^-1 Avd Ⅰ. In addition, 1 μmol·L^-1 Avd Ⅰ significantly decreased the apoptosis level, the B-cell lymphoma-2 associated X protein (Bax)/B-cell lymphoma-2 (Bcl-2) ratio and the cleaved cysteinyl aspartate specific proteinase 3 (cleaved caspase 3)/cysteinyl aspartate specific proteinase 3 (caspase 3) ratio. Therefore, Avd Ⅰ could stimulate the cardiomyocyte proliferation, reduce the LDH level and inhibit inflammation levels through regulating the mitochondrial apoptotic pathway.