The angle of His is the acute angle created between the cardia

Cardia

The cardia is the anatomical term for the part of the stomach attached to the esophagus. The cardia begins immediately distal to the z-line of the gastroesophageal junction, where the squamous epithelium of the esophagus gives way to the columnar epithelium of the gastrointestinal tract.Just...

 at the entrance to the stomach, and the oesophagus. It forms a valve, preventing reflux of duodenal bile

Bile

Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...

, enzymes and stomach acid from entering the oesophagus, where they can cause inflammation

Inflammation

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

. The angle is created by the collar sling fibres and the circular muscles around this (gastro-oesophagal) junction. The angle of His is normally undeveloped in infancy, with the oesophagus making a vertical junction with the stomach, and as a result, reflux of stomach contents is common.