Figure 2. Concentration-response curves (dashed lines) for the optical isomers and the racemate of bupivacaine on atrioventricular conduction time in 12 isolated perfused guinea pig hearts beating spontaneously. Data were analyzed using best-fit linear regression. Y intercepts are nearly identical in the three groups for an average of 62.7 ms; however, the average slope of the (+) bupivacaine group is more than double that of the (-) bupivacaine group, and the slope of the racemate lays between that of the isomers. Control values between the individual concentrations are not displayed. At 10 micro Meter only 2, 8, and 11 of 12 hearts treated with (+), (+), and (-) bupivacaine, respectively, remained in sinus rhythm and are displayed in this graph (see Figure 3).