Introduction: Laser has a widespread application in many sciences. There are many biological effects for laser. It causes lymphocytes increase, wounds healing, decrease of neural conduction and stimulation of collagen synthesis.
Methods: in order studying the helium neon laser effects on blood cells, electric activity of heart and spermatogenesis 35 male rats of the same age and same weight from Charz River race were divided into seven groups including sham and six experimental groups .Each group included five rats. Experimental groups 1,2 and 3 were exposed l0 mw laser radiation, for 10, 20 and 30 minutes and experimental groups 4,5 and 6 were exposed 20 mw, laser radiation for 10, 20 and 30 minutes respectively.
Results Statistic analysis showed that Helium-Neon laser on applied power and exposure duration did not have any significant effect on electrocardiographic parameters but has considerable effect on blood cells. So that white blood cells, red blood cells and platelets was decrease significantly and also causes the mean cell volume and mean cell hemoglobin to increase.
Conclusion: probably laser damage to bone marrow, which produce blood cells, and this results are an emphasis on physiological.