Abstract Tetramethylpyrazine (TMP) is the biologically active ingredient isolated from a popular Chinese medicinal plant, Ligusticum wallichil franchat, which has been used effectively since the 1970s to treat ischemic heart disease, cerebrovascular and thrombotic vascular diseases. The direct action of TMP on cardiac contractile function, however, is largely unclear. This study was designed to examine the effect of TMP on ventricular contractile function at the single cardiac myocyte level. Adult rat ventricular myocytes were isolated and stimulated to contract at 0.5 Hz, and mechanical and intracellular Ca 2+ properties were evaluated using an IonOptix Myocam system. Contractile properties analyzed included peak shortening (PS), time-to-peak shortening (TPS), time-to-90% relengthening (TR 90), maximal velocity of shortening/relengthening (±dl/dt), resting intracellular Ca 2+ level, Ca 2+-induced Ca 2+ release (CICR) and decay. TMP (10 −10–10 −5 M) exhibited an increase in PS with a maximal increase of 30.9%. TMP had no effect on ±dl/dt, TPS/TR 90 or CICR but lowered resting intracellular Ca 2+ level and slowed intracellular Ca 2+ decay. Pretreatment with either the nonspecific nitric oxide synthase (NOS) inhibitor Nω-nitro- l-arginine methyl ester ( l-NAME, 100 μM) or inducible NOS inhibitor W1400 effectively abolished the positive effect of TMP on myocyte shortening. Our data demonstrate a direct positive inotropic effect of TMP in cardiac myocytes, which may be related, at least in part, to NO production.