BACKGROUND: The synthetic narcotic sufentanil has been used in clinical practice for anesthetic induction and maintenance. But there is little information concerning its direct effects on heart. The purpose of this study is to evaluate the direct effects of sufentanil on contracture of ventricular myocardium. METHODS: Isometric contraction of isolated right ventricular papillary muscle of rabbit was measured under 0.2 Hz electrical stimulation in Krebs solution. Peak developed force(F), maximum rate of rise of developed force(+dF/dt(max)), maximum rate of fall of developed force(-dF/dt(max)) were analyzed. RESULTS: There were no statistically significant differences in frequency of isometric contraction from the 100% baseline value in time-matched control group. Sufentanil, in concentration of 0.01-0.1 mM, increased F, and -dF/dt(max) was decreased especially in concentration of 0.1 mM but not +dF/dt(max) Fo +dF/dt(max) and -dF/dt(max) were statistically different from time-matched control group in concentration of 0.1 mM. CONCLUSIONS: We conclude that sufentanil has mild contracture effect on ventricular muscle of rabbit directly.