A 60 year old woman presents with a retrosternal chest pain, associated with regurgitation of gastric acid into the mouth. A chest x-ray reveals an air fluid level overlying the cardiac shadow. Her body mass index is 34. What is the most likely diagnosis?
1) Gastroesophageal reflux disease (GERD)
2) Esophageal spasm
3) Peptic ulcer disease
4) Achalasia