Final answer:
The female patient's persistent epigastric pain that is not relieved by antacids, along with her elevated heart rate, suggests peptic ulcer disease as the most likely cause of her symptoms.
Step-by-step explanation:
Considering the symptoms of persistent epigastric pain, use of antacids without relief, and an elevated heart rate, the most likely cause of the female patient's symptoms is peptic ulcer disease (PUD). While conditions such as GERD, gallstones, and pancreatitis could have similar presentations, they typically would not result in persistent epigastric pain unresponsive to antacids. A peptic ulcer often presents with upper abdominal pain that can become more intense and may improve with eating, while antacids might offer temporary relief. If the pain does not subside with antacid use, this suggests that the ulceration may be significant, which warrants further medical evaluation beyond just lifestyle changes or simple antacid use.