Abstarct: Abstract Background and Objective: Physical activity causes structural and functional changes in the heart of athletes, especially the left ventricle, which depends on the intensity and duration of exercise. The present study investigates the effect of swimming duration on the exxpression of the left ventricular hypertrophy gene in male mice. Materials and Methods: 18 male mice (200± 20 g) were divided into three groups of control, medium and long-term swimming. Exercise groups (ten weeks and 5 days a week) swam in 28± 2 degrees water. In each session, the medium-term group swam for one hour and the long-term group from the fifth to the tenth week for three hours. Real-time PCR was used to measure the exxpression of purine genes bound to β-protein components, myocyte-enhancing factor 2C and histone-dastylase-4. Differences were determined by one-way ANOVA method and group comparisons were determined by Tukey post hoc test (p≤0.05). Results: In both exercise groups, compared to the control group, decreased exxpression of purine-attached genes to β-protein and histone-dastylase4 components, and decreased exxpression of myocyte-enhancing factor 2C genes were observed. Also, the exxpression of purine genes bound to β protein components and histone deacetylase 4 in the medium-term group increased significantly compared to the long-term group (p = 0.001). In addition, heart weight and heart weight / body surface area ratio in the medium and long-term swimming group increased significantly compared to the control group (p <0.05). Conclusion: It seems that ten weeks of swimming training can reduce the exxpression of MEF2C gene and also increase the exxpression of PURβ and HDAC4 genes, and since these exercises increase the weight variables of the heart, ventricle Left and related indicators are effective. Therefore, swimming for long periods of time can be recommended as an important strategy for improving and functioning of the heart.