The reproducibility of carotid sinus hypersensitivity to carotid sinus massage was studied in the long-term follow-up of 8 patients with carotid sinus syndrome. A cardioinhibitory response was induced in 7 patients, while a vasode-pressor response was found in the remaining patient. The 7 patients were treated with dual-chamber pacemaker implantation and the remaining patient was treated with propranolol. All of the patients remained asymptomatic during a follow-up period of 48±11 months. Carotid sinus massage during the follow-up period in patients with a cardioin-hibitory response revealed asystolic intervals of 3s or longer in 4 patients and in 3 patients at the second and third follow-up examinations, respectively, although there were no significant differences in the ventricular asystolic intervals between before, and 34±11months and 48±11months after treatment. However, each patient showed a wide variation in asystolic intervals. The differences in asystolic intervals between prior to treatment (first) and the third test were significantly greater than those between the first and the second test (2.4±1.2s vs 0.7±0.6s ; p<0.05). The one patient with a vasodepressor response had a decreased systolic blood pressure greater than 50 mmHg by carotid sinus massage at all three occasions. In conclusion, most patients with carotid sinus syndrome showed abnormal and variable responses to carotid sinus massage during long-term follow-up period although there was no recurrence of symptoms after treatments. The lack of symptoms in these patients was believed to have been due to effective treatment with dual-chamber pacing and β-blocker, rather than to spontaneous remission.