The present study was aimed to explore pathophysiological implications of nitric oxide in the development of left and right ventricular hypertrophy. To induce selective left and right ventricular hypertrophy, rats were made two-kidney, one clip (2K1C) hypertensive and treated with monocrotaline (MCT), respectively. Six weeks later, the hearts were taken and their ventricular tissue mRNA and protein expression of endothelial constitutive isoform of nitric oxide synthase (NOS) were determined by reverse transcription-polymerase chain reaction and Western blot analysis, respectively. In 2K1C hypertensive rats, the expression of NOS mRNA was increased in parallel with its proteins in the left ventricle, but not in the right ventricle. In MCT-treated rats, the expression of NOS mRNA and proteins were proportionally increased in the right ventricle, but not in the left ventricle. These results suggest that the expression of NOS is specifically increased in association with the ventricular hypertrophy, which may be a mechanism counteracting the hypertrophy.