To assess left atrial appendage (LAA) function in hypertensive patients without treatment, transesophageal echocardiography (TEE) was performed in 46 hypertensive patients in sinus rhythm, aged 40 to 55 years, and in 16 control subjects (group I) without cardiovascular disease, aged 41 to 54 years. The hypertensive patients were divided into 2 groups according to left ventricular (LV) systolic function: group II, the group with normal LV systolic function (ejection fraction 0.63 +/- 0.08), and group III, the group with LV systolic dysfunction (ejection fraction 0.39 +/- 0.05). The LAA late emptying velocities (EVs) were significantly reduced in the hypertensive subgroups compared with the control group (P < .001), but no significant difference in the LAAEV was found between groups Il and III. The LAAEV in the hypertensive patients had a significant negative correlation with diastolic blood pressure, systolic blood pressure, and left atrial (LA) diameter. The maximal LAA areas were significantly larger in the hypertensive subgroups than in the control group (P < .05). No significant difference in LAA maximal area existed between groups II and III. The maximal LAA area in the hypertensive patients had a significant positive correlation with diastolic blood pressure, systolic blood pressure, and LA diameter, but a significant negative correlation with LV ejection fraction. With TEE, LA spontaneous echocardiographic contrast (SEC) was present in 6 (43%) of 14 patients in group III (P < .01) and in 7 (22%) of 32 patients in group II (P < .05). No significant difference in the occurrence of LASEC was found between groups II and III. Left atrial appendage thrombi by TEE were observed in 4 (29%) of 14 patients in group III (P < .05) and in 4 (13%) of 32 patients in group II (P = not significant). No significant difference in the occurrence of LAA thrombus existed between groups II and III. In conclusion, in patients with untreated hypertension, marked elevation of afterload imposed on the left atrium may involve both the left atrium and the LAA, resulting in impairment of LAA function. This condition may worsen with subsequent occurrence of SEC and later, thrombus formation. Therefore assessment of LAA function may be important even in the hypertensive patient in sinus rhythm.