This study investigates the role of mitochondrial-derived methylmalonic acid (MMA) in myocardial ischemia–reperfusion (I/R) injury and its mechanism of action. Key findings include: 1. **MMA Accumulation and Injury**: - MMA levels are significantly increased in patients with acute myocardial injury and in cardiomyocytes under hypoxia/reoxygenation (H/R) conditions. - MMA treatment exacerbates myocardial oxidative stress and ferroptosis, leading to larger myocardial infarct size and cardiac dysfunction in mice with I/R injury. 2. **Mechanisms of MMA-Induced Injury**: - MMA promotes NOX2/4 expression, increasing reactive oxygen species (ROS) production, which activates ferroptosis. - Increased ROS inhibits solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4) expression, further exacerbating ferroptosis. - MMA decreases the nuclear distribution of nuclear factor E2-related factor 2 (NRF2) by enhancing its interaction with kelch-like ECH-associated protein 1 (KEAP1), impeding GPX4/SLC7A11 activation. 3. **Antioxidant and Ferroptosis Inhibitors**: - N-acetylcysteine (NAC) alleviates MMA-induced injury by reducing oxidative stress and ferroptosis. - Ferrostatin-1 (FER-1) and RSL3, ferroptosis inhibitors, show opposite effects on cardiac function and infarct size, supporting the role of ferroptosis in MMA-induced injury. 4. **Conclusion**: - MMA plays a crucial role in myocardial injury under I/R stress by inducing oxidative stress and ferroptosis. - The interaction between NRF2 and KEAP1 is a key mechanism in MMA-induced ferroptosis. - These findings provide new insights into the pathogenesis of I/R injury and potential therapeutic targets. This study highlights the importance of MMA in myocardial injury and suggests that targeting oxidative stress and ferroptosis may be a promising approach for treating I/R injury.This study investigates the role of mitochondrial-derived methylmalonic acid (MMA) in myocardial ischemia–reperfusion (I/R) injury and its mechanism of action. Key findings include: 1. **MMA Accumulation and Injury**: - MMA levels are significantly increased in patients with acute myocardial injury and in cardiomyocytes under hypoxia/reoxygenation (H/R) conditions. - MMA treatment exacerbates myocardial oxidative stress and ferroptosis, leading to larger myocardial infarct size and cardiac dysfunction in mice with I/R injury. 2. **Mechanisms of MMA-Induced Injury**: - MMA promotes NOX2/4 expression, increasing reactive oxygen species (ROS) production, which activates ferroptosis. - Increased ROS inhibits solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4) expression, further exacerbating ferroptosis. - MMA decreases the nuclear distribution of nuclear factor E2-related factor 2 (NRF2) by enhancing its interaction with kelch-like ECH-associated protein 1 (KEAP1), impeding GPX4/SLC7A11 activation. 3. **Antioxidant and Ferroptosis Inhibitors**: - N-acetylcysteine (NAC) alleviates MMA-induced injury by reducing oxidative stress and ferroptosis. - Ferrostatin-1 (FER-1) and RSL3, ferroptosis inhibitors, show opposite effects on cardiac function and infarct size, supporting the role of ferroptosis in MMA-induced injury. 4. **Conclusion**: - MMA plays a crucial role in myocardial injury under I/R stress by inducing oxidative stress and ferroptosis. - The interaction between NRF2 and KEAP1 is a key mechanism in MMA-induced ferroptosis. - These findings provide new insights into the pathogenesis of I/R injury and potential therapeutic targets. This study highlights the importance of MMA in myocardial injury and suggests that targeting oxidative stress and ferroptosis may be a promising approach for treating I/R injury.