Purpose: Whether or not right and left stellate ganglion blocks (SGB) affect blood pressure (BP) and heart rate (HR) differently has been controversial. The aim of this study was to analyze BP and HR changes after large numbers of right or left SGBs. Methods: A total of 16,404 right SGBs and 13,766 left SGBs were performed with 6 ml of 1% mepivacaine using the anterior paratracheal approach at C6. Changes in systolic BP and HR 30 min after SGBs were compared to the baseline values. Results: Systolic BP decreased by 25 to 49 mmHg in 10.93% and more than 50 mmHg in 0.67% of 16,404 right SGBs. Those percentages were significantly higher than corresponding percentages; 8.43% and 0.49% of 13,766 left SGBs (P < 0.0001 and P < 0.05, respectively). On the other hand, systolic BP increased by 25-49 mmHg in 5.74% and more than 50 mmHg in 0.52% of left SGBs, and in 4.15% and 0.18% of right SGBs (P < 0.0001and P < 0.0001 between left and right SGBs, respectively). Right SGB caused marked reduction in HR (greater than 30 beats/min), more than left SGB (4.22% versus 2.70%, P < 0.0001). Conclusions: Both right and left SGBs could produce clinically significant hypertension and hypotension, and also severe bradycardia. However, right SGB produces a higher incidence of significant reductions in systolic BP and HR, compared to left SGB. On the other hand, left SGB produces a significant increase in systolic BP compared to right SGB. Those differences likely stem from the hemispheric asymmetry in autonomic cardiovascular control.