Ginseng, the root of Panax ginseng, has been used as folk medicine in the treatment of various diseases for thousands of years in China.Ginsenoside Rb1(Rb1), one of the effective components of ginseng, has been reported to release nitric oxide and decrease intracellular free Ca2+ in cardiac myocytes, both of which play important roles in antihypertrophic effect.This study was to investigate the potential effect of Rb1 on right ventricular hypertrophy (RVH) induced by monocrotaline (MCT) and its possible influence on calcineurin (CaN) signal trasnsduction pathway.MCT-treated animals were administered with Rb1 (10 and 40 mg /kg) from day 1 to day 14 (preventive administration) or from day 15 to day 28 (therapeutic administration), or with vehicle as corresponding controls.After 2 weeks, significantly hypertrophic reactions, including RVH index and the expressions of atrial natriuretic peptide mRNA, appeared in right ventricle of all MCT-treated animals (p<0.05), which were significantly decreased with some improvements of myocardial pathomorphology in both Rb1 prevention- and therapy-groups(p<0.05).Similarly, MCT-treatment caused the high expressions of mRNA and/or proteins of CaN, NFAT3 and GATA4 from cardiocytes(p<0.05)and Rb1 could alleviate the expressions of these factors above (p<0.05).These results suggest that Rb1 treatment can inhibit the RVH induced by MCT, which may be involved in its inhibitory effects on CaN signal transduction pathway.