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Objective To discuss the mechanism about exercise preconditioning (EP) protected myocardium by means of regulate NLRP3 inflammasome signal pathways on exhausted exercise rats. Methods The male Sprague-Dawley (SD) rats were randomly divided into four groups: normal control group (C group), no EP on exhausted exercise group (EE group), 3dEP + EE group, and 3wEP + EE group, with 12 rats in each group. In C group and EE group, the rats had not done exercise, while EE group took an exhausted swimming exercise with 3% heavy weight on tail at the end of 3 weeks; 3dEP + EE group and 3wEP + EE group exercised according to the standard of swimming for 60 minutes every day (swam 15 minutes, took a rest for 5 minutes, repeated 3 times), 6 days in a week, and were trained for 3 days and 3 weeks respectively, and took an exhausted swimming exercise on the last day. A light microscope and electron microscope were used to observe the myocardial histopathology and ultrastructure change, and enzyme linked immunosorbent assay (ELISA) was used to detect the levels of serum interleukin (IL-1β, IL-18, IL-6), hypersensitive C-reactive protein (hs-CRP), MB isoenzyme of creatine kinase (CK-MB), and brain natriuretic peptide (BNP). The protein expressions of NLRP3 and caspase-1 were detected by Western Blot. The correlations among all the parameters were analyzed by Pearson correlation analysis. Results Under the light microscope and electron microscope, the myocardial fiber morphological structure was normal, neatly, and no interstitial edema, muscle membrane damage or myocardial cell swellen was found in C group. In EE group, heart tissues were stained obviously uneven, a large number of myocardial fibers were fractured and messed, interstitial fibers were hyperplasiaed and edema moderately, much of myocardial cells were edema and necrosis, inflammatory cells were infiltrated, the number of average infiltration inflammatory cells was highest, mitochondria were edema seriously, part of the crest and a small number of membrane were blended together, fuzzy and crest were fractured, sarcomere were disordered; 3dEP + EE group and 3wEP + EE group heart tissues injuries were obviously alleviated, among the three groups, and the best results were in 3wEP + EE group. Compared with C group, the serum contents of IL-1β, IL-18, IL-6, hs-CRP, CK-MB, BNP and heart tissues protein expressions of NLRP3 and caspase-1 in EE group were significantly increased [IL-1β (μg/L): 18.77±1.28 vs. 12.00±1.55, IL-18 (μg/L): 236.79±15.73 vs. 150.74±7.09, IL-6 (μg/L): 59.31±9.17 vs. 34.65±2.89, hs-CRP (mg/L): 469.37±137.73 vs. 107.15±14.22, CK-MB (U/L): 15.57±0.91 vs. 7.40±0.40, BNP (ng/L): 532.08±63.44 vs. 386.96±34.77, NLRP3 protein (gray value): 0.66±0.07 vs. 0.16±0.06, caspase-1 protein (gray value): 0.96±0.08 vs. 0.48±0.06, all P < 0.01]. Compared with EE group, the above indicators in 3dEP + EE group and 3wEP + EE group were remarkably decreased, each index in 3wEP + EE group was lower than that in 3dEP + EE group except BNP [IL-1β (μg/L): 14.26±1.42 vs. 16.57±1.81, IL-18 (μg/L): 168.49±7.05 vs. 191.92±14.16, IL-6 (μg/L): 32.62±3.81 vs. 45.61±6.20, hs-CRP (mg/L): 207.06±41.68 vs. 339.56±89.65, CK-MB (U/L): 9.97±1.08 vs. 13.10±0.78, NLRP3 protein (gray value): 0.33±0.07 vs. 0.48±0.06, caspase-1 protein (gray value): 0.65±0.06 vs. 0.79±0.02, all P < 0.01; BNP (ng/L): 432.53±32.03 vs. 478.46±44.79, P > 0.05]. A positive correlation was shown among IL-1β, IL-18, IL-6, hs-CRP, BNP, CK-MB, NLRP3, and caspase-1 (all P < 0.01). Conclusions EP can reduce inflammatory reaction by regulating the NLRP3 inflammatory signal pathways, and protect the myocardial injury. The protection of the heart by long-term EP is more obvious than that of short-term EP.