Background. Cardiac ischemia reperfusion (I/R) injury is associated with overproduction of reactive oxygen species (ROS). Low frequency pulse magnetic fields (LFMFs) have been reported to decrease ROS generation in endothelial cells. Whether LFMFs could assert protective effects on myocardial from I/R injury via ROS regulation remains unclear. Methods. To simulate in vivo cardiac I/R injury, neonatal rat cardiomyocytes were subjected to hypoxia reoxygenation (H/R) with or without exposure to LFMFs. Cell viability, apoptosis index, ROS generation (including and ONOO？), and NO production were measured in control, H/R, and H/R + LFMF groups, respectively. Results. H/R injury resulted in cardiomyocytes apoptosis and decreased cell viability, whereas exposure to LFMFs before or after H/R injury significantly inhibited apoptosis and improved cell viability ( ). LFMFs treatment could suppress ROS (including and ONOO？) generation induced by H/R injury, combined with decreased NADPH oxidase activity. In addition, LFMFs elevated NO production and enhanced NO/ONOO？ balance in cardiomyocytes, and this protective effect was via the phosphorylation of endothelial nitric oxide synthase (eNOS). Conclusion. LFMFs could protect myocardium against I/R injury via regulating ROS generation and NO/ONOO？ balance. LFMFs treatment might serve as a promising strategy for cardiac I/R injury. 1. Introduction Acute coronary syndrome, including acute myocardial infarction (AMI), is one of the major causes of morbidity and mortality for patients with coronary heart diseases worldwide [1]. Effective reperfusion therapies like percutaneous coronary intervention (PCI) and coronary artery bypass grafting (GABG) could reduce myocardial ischemia, which in turn minimize myocardial infarction size and improve patients’ prognosis [2]. Reperfusion strategies are necessary to resuscitate the ischemic myocardium; however, they may result in paradoxical cardiomyocyte dysfunction and aggravate tissue damage, a process termed as “reperfusion injury” [3]. Thus, an effective strategy to protect heart against ischemia reperfusion (I/R) injury is imperative for successful treatment of coronary heart diseases. Low-frequency magnetic fields (LFMFs) are considered to be therapeutic and have been started to be applied more and more commonly in medicine. Many studies have demonstrated that LFMFs are capable of affecting a number of physiological and pathological processes. The protective effects of LFMFs on heart tissue against I/R injury have also been widely studied. It is reported that exposure to
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