In the first and second parts of this study, 5-hydroxytryptamine (5HT) receptors, including 5-HT3 and 5-HT4 with the highest expression level, were found in clasp and sling fibres of the lower esophageal sphincter (LES). Specific 5-HT3 and 5-HT4 receptor agonists can induce the contraction effect of clasp and sling fibres of the LES while specific 5-HT7 receptor agonists showed no effects. In the study of this part, the in-vitro muscle tension measurement technology and EFS methods were used to detect the effect of the selective 5-HT receptor antagonist on the clasp and sling fibres of the in-vitro LES under the electrical field stimulation (EFS), and further to ensure the effect of 5-HT receptor in the LES neuroregulatory pathway, and deeply explore the effect of 5-HT receptor in the systolic and diastolic function regulation of the LES.