Aim To observe expressional change of proliferating cell nuclear antigen(PCNA) and cyclin D1 of cardiomyocytes in hypertrophic myocardium induced by pressure overload and investigate the relationship between cardiomyocytes hyperplasia and myocardial hypertrophy. Methods Rat models of pressure overload were produced by aorta constriction(AC). Myocardial mechanics were measured by carotid artery canal connected with pressure transducer and the changes of LV/Bwt and myocardium transverse diameter(TDM) were determined. The expressions of PCNA and cyclin D1 were detected by immunohistochemical method and the ratio of positive cardiomyocytes nuclear and total cardiomyocytes nuclear were then calculated. Result Myocardial mechanics and left ventricular mass index of AC group were significantly higher than that of matchable SO group (p<0.05), and progressively increased in 1, 3, 6 weeks after AC. A significant increase of positive ratios of PCNA and cyclin D1 followed by a gradual decline from it peak in the 1st week to normal in 6th week after AC were observed. Conclusion There were not only the enlarging of cellular size but also the higher expression of proliferation marker in early stage of myocardial hypertrophy. This expression of proliferation marker gradually fall to normal level along with the adaption of heart to pressure overload, while the cardiomyocytes size remained progressive enlargement.