Objectives To investigate the relation between hypertrophied myocardium and ventricular fibrillation threshold in spontaneously hypertensive rats (SHR). Methods 20 male SHR were randomly divided into two groups; 10 week group (n = 10) and 18 week group (n=10). 10 week male Wistar rats were controlled group (n=10). The systolic blood pressure (SBP), heart mass index (HMI), ventricular effective refractory period (VERP) and ventricular fibrillation threshold(VFT) were measured respectively. Results①The SBP and HMI of SHR were significantly higher than those of Wistar rats(P < 0.001). The VFT of SHR were significantly lower than that of Wistar rats (P < 0.001).②In SHR, the SBP and HMI of 18 week SHR were significantly higher than those of 10 week SHR (P< 0.001). The VFT of 18 week SHR were significantly lower than that of 10 week SHR (P < 0.001).③There were no significant difference of VERP among 10 week SHR, 18 week SHR and Wistar rats(P > 0.05).④There was no relationship between HMI and VFT or SBP in Wistar rats. There was significant relationship between HMI and VFT or SBP in different age spontaneously hypertensive rats.⑤HMI, age and species of animal were the major influent factors of VFT. Conclusions The VFT of hypertrophied myocardium decreased. The higher the degree of hypertrophy of myocardium and the higher the systolic blood pressure were, the lower the ventricular fibrillation threshold was. Objectives To investigate the relation between hypertrophied myocardium and ventricular fibrillation threshold in spontaneously hypertensive rats (SHR). Methods 20 male SHR were randomly divided into two groups; 10 week group (n = 10) and 18 weeks group (n = 10) week systolic blood pressure (SBP), heart mass index (HMI), ventricular effective refractory period (VERP) and ventricular fibrillation threshold (VFT) were measured respectively. Results①The SBP and HMI of SHR were significantly higher than those of Wistar rats (P <0.001). The VFT of SHR were significantly lower than those of Wistar rats The VFT of 18 weeks SHR was significantly lower than that of 10 weeks SHR (P <0.001). ③ There was no significant difference of VERP among 10 weeks SHR, 18 weeks SHR and Wistar rats ( P> 0.05) .④There was no relationship between HMI and VFT or SBP in Wistar rats. There was significant relationship between HMI and VFT or SBP in different age spontaneously hypertensive rats. ⑤ HMI, age and species of animal were the major influent factors of VFT. Conclusions The VFT of hypertrophied myocardium decreased. higher the degree of hypertrophy of myocardium and the higher the systolic blood pressure were, the lower the ventricular fibrillation threshold was.