Historical studies demonstrating differential effects between left and right sympathetic outflows to the heart have employed canine models (Ardell et al, 1988). The aim of this study was to re-examine these differences in the rabbit using a novel in vitro preparation. Adult male New Zealand rabbits (3.0±0.1kg; n=4) were used. The isolated heart preparation with intact autonomic nerves was obtained under propofol anaesthesia (1 mg/kg, i.v.) as previously described (Ng et al, 2001). Left ventricular pressure (LVP) was measured using a fluid filled balloon. The left and right paravertebral sympathetic chains were identified and isolated from adjacent tissues from the level of T4 up to T1/2 where fine custom-made silver bipolar electrodes were positioned and electrically isolated with dental cement. The threshold voltage that caused an increase in both heart rate (HR) and LVP was determined and left (LS) and right (RS) sympathetic chains were stimulated separately at twice threshold voltage at 2.3±1.1V (LS) and 1.2±0.4V (RS) respectively at 2Hz [Low], 5Hz [Med] and 10Hz [High] during 1) sinus rhythm and 2) during right ventricular pacing at 250bpm to examine chronotropic and inotropic effects. Data are mean±SEM, statistical analysis was performed using 2-factor ANOVA. Results: LS and RS increased both HR and LVP, to differing degrees (Fig1A). The peak HR achieved during RS was significantly greater than during LS (Table 1). Whilst there was a trend for LS to have a greater effect in increasing LVP than RS (see Table 1 and Fig1B). 2-factor ANOVA revealed a significant difference in the percentage change in HR and LVP between LS and RS (Fig1B). In conclusion, stimulating the right sympathetic outflow to the heart has a more prominent effect on the sino-atrial node but a weaker effect on the left ventricle, whereas the reverse is true when stimulating the left sympathetic outflow. This may reflect regional differences on sympathetic innervation to the heart.