Spinal injection of small-dose (SD) bupivacaine decreases the likelihood of hypotension compared with large-dose (LD) bupivacaine. We assumed that a SD of bupivacaine could also prevent the decrease in cardiac output (CO). Patients undergoing elective urologic, lower abdominal, or lower limb surgery under spinal anesthesia were included in this prospective randomized study. Spinal injection consisted of 5 mug of sufentanil and either SD (7.5 mg of hyperbaric bupivacaine with glucosemonohydrate 80 mg/mL; n = 19 patients) or LD (12.5 mg of hyperbaric bupivacaine with glucosemonohydrate 80 mg/mL; n = 19 patients). CO (impedance cardiography), arterial blood pressure, and heart rate) were measured at 1 min before performance of spinal block and 2, 10, and 30 min after the intrathecal injection. Sensory level was also assessed at 30 min. CO was higher in the SD group as compared with the LD group from 2 min to 30 min after spinal anesthesia. Moreover, CO increased at 2 min in the SD group and decreased at 10 and 30 min in the LD group compared with baseline value. In conclusion, SD bupivacaine provides successful anesthesia and gives better CO stability than LD.