Objective To investigate the cardioprotective effect of electroacupuncture in rats with acute myocardial ischemia, the effect of its duration on the expression level of nuclear factor- kappa B (NF- κB) in myocardium, and the mechanism of electroacupuncture in the intervention of acute myocardial ischemia. Methods Sprague- Dawley rats were randomly divided into normal group, model group, immediate electroacupuncture group, and 1- , 3- , 5- , and 7- day electroacupuncture groups, with 6 rats in each group. Ligation of the left anterior descending coronary artery was performed to establish a rat model of acute myocardial ischemia. Electroacupuncture was performed at the "Shenmen- Tongli" segment of the heart meridian for 30 minutes each time, and interrupted wave with a frequency of 2 Hz and an intensity of 1 mA was used to perform immediate electroacupuncture and electroacupuncture for 1, 3, 5, and 7 days. The PowerLab 16- lead physiological recorder was used to record electrocardiogram; ELISA was used to measure the serum levels of creatine kinase (CK), creatine kinase isoenzyme (CK- MB), and ischemia- modified albumin (IMA); Western blot and quantitative real- time PCR were used to measure the protein and mRNA expression levels of NF- κB in myocardial tissue. Results Compared with the normal group, the model group had ST- segment elevation and significant increases in the serum levels of CK, CK- MB, and IMA (P<0.05) and the protein and mRNA expression levels of NF- κB (P<0.05). There was no significant difference in the serum level of IMA between the model group and the immediate electroacupuncture group (P>0.05), and compared with the model group, the immediate electroacupuncture group had significant reductions in the levels of CK and CK- MB (P<0.05), while the levels of CK, CK- MB, and IMA gradually decreased in the other electroacupuncture groups, with the greatest reductions in the 7- day electroacupuncture group (P<0.05). There were no significant differences in the protein and mRNA expression levels of NF- κB in myocardial tissue between the immediate electroacupuncture group and the 1- day electroacupuncture group (P>0.05), and the 1- , 3- , 5- , and 7- day electroacupuncture groups had reductions in the protein and mRNA expression levels of NF- κB, with the greatest reductions in the 7- day electroacupuncture group (P<0.05). Conclusion Electroacupuncture at the heart meridian improves acute myocardial ischemia since day 3 of acupuncture and shows the most significant effect after 7 days of treatment, possibly by reversing the expression of NF- κB in myocardial tissue.