To investigate the underlying mechanisms of cyclovirobuxinum D (Cvb-D) on alleviating cardiac hypertrophy in rats. Sprague-Dawley rats were randomly divided into 5 groups: control group; levothyroxine-induced cardiac hypertrophy group (model); levothyroxine-induced cardiac hypertrophy + Cvb-D group (Cvb-D); levothyroxine-induced cardiac hypertrophy + captopril group (captopril); levothyroxine-induced cardiac hypertrophy + SB203580 group (SB203580), n=10 for each group. Rats were daily administered the respective drugs continuously for14 days by gastric gavage. A rat model of cardiac hypertrophy was established by intraperitoneal injection of levothyroxine to investigate whether Cvb-D protects against cardiac hypertrophy by inhibiting the p38 mitogen-activated protein kinase (MAPK) signaling pathway and preventing apoptosis of cardiac cells. Treatment with Cvb-D significantly deceased left ventricle hypertrophy, improved the histopathology, hemodynamic conditions, and cardiac function in rats with cardiac hypertrophy. Compared with the normal control group, in rats with cardiac hypertrophy, expression of bax in the heart and phospho-p38 MAPK protein levels were significantly up-regulated (P < 0.01 or 0.05), whereas the bcl-2 protein level was down-regulated (P < 0.01). In contrast, Cvb-D treatment reversed the changes in bax and phospho-p38 MAPK protein levels but increased the bcl-2 protein level (P < 0.01 or 0.05), and these effects were similar to those of captopril and SB203580 (a specific p38MAPK inhibitor) treatment. Furthermore, both Cvb-D, captopril and SB203580 reduced mRNA expression of p38 alpha, p38 beta, c-fos, and c-jun mRNA, and Cvb-D had a stronger effect (P < 0.01). These results demonstrate that Cvb-D protects against cardiac hypertrophy, which is possibly mediated by prevention of cardiac cell apoptosis and inhibition of the p38MAPK signaling pathway.