While functional heartburn (FH) and functional dyspepsia (FD) are recognized clinical entities, symptoms often overlap across both disorders. Despite their frequency, little is known of the underlying pathophysiology of overlapping symptoms. This study evaluated the effect of the 5-HT(4) agonist, tegaserod, on visceral sensitivity and symptom improvement in patients with overlapping symptoms of FH and FD.Patients with overlapping symptoms of FH and FD (ROME II) and mechanical hypersensitivity (Barostat examination) were randomized to tegaserod 6 mg bid or placebo for 2 weeks with treatment crossover after a 2-week washout period. Esophageal and gastric Barostat sensory tests were performed and patients rated their overall symptoms at study end. When carry-over was detected, data were presented for period 1 only. Safety was also assessed.Sixty patients were screened of whom 30 were randomized and 25 completed. Mechanical hypersensitivity was reported by 83% of 47 patients completing esophageal and gastric baseline Barostat examinations. Tegaserod did not significantly alter balloon volume to pain (primary variable); however, pressure to gastric pain increased (p = 0.044 vs. placebo). The severity of heartburn, regurgitation, early fullness, and bloating was significantly lower following tegaserod vs. placebo treatment (p = 0.026, p = 0.021, p = 0.016, and p = 0.030). Overall symptom improvement was reported by 52% tegaserod vs. 32% placebo patients (p = 0.275), and treatment was well tolerated.Results suggest that tegaserod may increase the gastric pain threshold and decrease the severity of individual symptoms in patients with overlapping FH and FD. However, these findings must be considered within the context of the study limitations, including the small number of subjects, potential for and presence of a carry-over effect, along with the impact of Barostat balloon use on the assessment of gastric function.