If someone has pyrosis, what medical condition do they have?

 GERD.

Pyrosis is a symptom of GERD (gastroesophageal reflux disease), which is a condition in which stomach acid flows back up into the esophagus. The stomach acid can cause a burning sensation in the chest (pyrosis) and throat. Other symptoms of GERD include heartburn and regurgitation. Treatment for GERD usually involves lifestyle changes, such as avoiding certain foods and drinks that trigger symptoms, and medications such as proton pump inhibitors or H2 blockers.