Fundoplication efficacy is a tradeoff between protection against reflux and post-operative dysphagia from the surgically altered mechanical balance within the esophago-gastric segment. AIM: To contrast quantitatively the mechanical balance between normal and post-fundoplication esophageal emptying. METHODS: Physiological data were combined with mathematical models based on the laws of mechanics. Seven normal controls (NC) and 7 post fundoplication (FP) patients underwent concurrent manometry and fluoroscopy. Temporal changes in geometry of the distal bolus cavity and hiatal canal, and cavity driving pressure were quantified during emptying. Mathematical models were developed to couple cavity pressure to hiatal geometry and esophageal emptying, and to determine cavity muscle tone. RESULTS. The average length of the hiatal canal post FP was twice that of NC; reduction of hiatal radius was not significant. All esophageal emptying events post FP were incomplete (51% retention), there was no significant difference in the period of emptying between NC and FP, and average emptying rates were 40% lower post FP. The model predicted three distinct phases during esophageal emptying: hiatal opening (I), a quasi-steady period (II), and final emptying (III). A rapid increase in muscle tone and driving pressure forced normal hiatal opening. Post FP there was a severe impairment of cavity muscle tone causing deficient hiatal opening and flow, and bolus retention. CONCLUSIONS: Impaired esophageal emptying post-FP follows from the inability of distal esophageal muscle to generate necessary tone rapidly. Immobilization of the intrinsic sphincter by the surgical procedure may contribute to this deficiency, to impaired emptying and, possibly, dysphagia.