This chapter reports a case of functional heartburn in a female in her 60s. Approximately 6 months ago, her heartburn worsened. Upper gastrointestinal endoscopy confirmed the diagnosis of NERD, and she was treated with potassium-competitive acid blocker (P-CAB) vonoprazan fumarate without symptom improvement, prompting her to seek further evaluation and treatment. High-resolution manometry (HRM) and high-resolution impedance manometry (HRIM) showed no evidence of esophageal motility disorders. After discontinuing potassium-competitive acid blocker (P-CAB), 24-hour esophageal multichannel intraluminal impedance pH (MII-pH) monitoring was performed, and both the symptom index (SI) and symptom-associated probability (SAP) were negative. Since both SI and SAP were negative, the patient was diagnosed with functional heartburn. Due to resistance to acid-suppressing drugs, anxiolytic tandospirone citrate was administered, and its efficacy was confirmed. Psychological factors may also be involved in functional heartburn.