Objective: To investigate the functional carrelation between cardiogenic referred pain and Heart Meridian of Traditional Chinese Medicine.Methods: Eighteen SD rats anesthetized with 10% urethane(1 g/kg) were used in this study.For observing somato-sympathetic reflex activity

the cardiac sympathetic nerve(CSN) was isolated and its electrical activities were recorded by using a bipolar platinum electrode;and bipolar stimulating electrodes were separately inserted into "Qingling" (HT 2)

"Shaohai"(HT 3) of the Heart Meridian

and "Xiabai"(LU 4) and "Chize" (LU 5) of the Lung Meridian on the forearm.For observing sympathosomatic reflex

the recording electrode hooking CSN was used as the stimulating electrode

and reflex myoelectric activity of "Qingling"(HT 2)

"Shaohai"(HT 3)

"Xiabai"(LU 4) and "Chize"(LU 5) were recorded respectively by using a pair of stainless steel electrodes.Results: The excitement threshold of CSN activity upon electrical stimulation of HT 2 and HT 3 on the left side was significantly lower than that of stimulation of LU 4 and LU 5 on the same side(P<0.05);correspondingly

the CSN firing rates responding to electrical stimulation(4 mA) of HT 2 and HT 3 were significantly higher than those responding to electrical stimulation(4 mA) of LU 4 and LU 5 on the same side.It indicated that the response sensitivity of CSN to stimulation of the Heart Meridian was evidently stronger than that of electrical stimulation of the Lung Meridian.Following electrical stimulation(2-6 mA) of CSN

the reflex muscular electric activity of HT 2 and HT 3 was also stronger than that of electrical stimulation(same one strength) of LU 4 and LU 5 on the same side(P<0.01).Furthermore

the response threshold of myoelectrical activity of HT 2 and HT 3 upon electrical stimulation of CSN was significantly lower than that of LU 4 and LU 5(P<0.01).Conclusion: These findings showed that acupoints of the Heart Meridian have a closer correlation with CSN on the same side compared with those of Lung Meridian

which may be one of the causes that acupoints of the Heart Meridian are often used to treat cardiac disorders in clinical practice and cardiogenic referred pain often appears in the running course of Heart Meridian on the forearm.