hiatal hernia ; Causes hiatal hernia

Your chest cavity and abdomen are separated by your diaphragm — a large dome-shaped muscle that's responsible for a good part of normal breathing. Your esophagus passes into your stomach through an opening in the diaphragm. Hiatal hernias occur when the muscle tissue surrounding this opening becomes weak and the upper part of your stomach bulges through the diaphragm into your chest cavity. Anything that puts intense pressure on your abdomen — including persistent or severe coughing or vomiting, pregnancy, straining while going to the bathroom, or lifting heavy objects — can contribute to hiatal hernias.

A hiatal hernia in turn can cause or contribute to gastroesophageal reflux.
This happens when a hernia slightly displaces the lower esophageal sphincter, a circular band of muscle around the bottom of the esophagus.

Ordinarily, the diaphragm is aligned with the lower esophageal sphincter, which relaxes to allow food and liquid to flow into your stomach when you swallow. The diaphragm supports and puts pressure on the sphincter to keep it closed when you're not swallowing. But a hiatal hernia raises the sphincter above the diaphragm, reducing pressure on the valve. This causes the sphincter muscle to open at the wrong time, allowing stomach acid to flow up into the esophagus.

A hiatal hernia can also cause heartburn if the herniated portion of your stomach becomes a reservoir for gastric acid, which can then easily travel up your esophagus.
When to seek medical advice
Many people discover they have hiatal hernias when they see their doctors about heartburn. Most cases of heartburn are mild and temporary. But if your symptoms are severe, occur often, or are accompanied by coughing, wheezing, asthma, a sore throat, difficulty swallowing or chest pain, talk to your doctor.

If you know you have a large hiatal hernia and experience severe chest pain, difficulty breathing or trouble swallowing, seek medical care immediately.

http://www.mayoclinic.com/health/hiatal-hernia/DS00099/DSECTION=4