Abstract: Objective To investigate the changes of plasma hydrogen sulfide (H₂S) in patients with coronary heart disease (CHD). Methods Plasma H₂S levels were measured in 40 patients with CHD and 17 angiographically normal patients by sulfide-sensitive electrodes, and the variation of plasma H₂S levels was analyzed in different clinical types of CHD and in different types of coronary artery lesions. The association of plasma H₂S levels with the risk factors of CHD was also analyzed. Results Plasma H₂S levels were significantly lowered in CHD patients in comparison with that in angiographically normal control subjects (26.10±14.27 μmol/L vs 51.74±11.94 μmol/L, P<0.001). In CHD patients, plasma H₂S levels in unstable angina patients (UAP, 23.60±14.41 μmol/L) and acute myocardial infarction patients (AMI, 19.98±7.516 μmol/L) were significantly lower than that in stable angina patients (SAP, 38.41±14.53 μmol/L, P<0.05). No significant difference in plasma H₂S levels was found between CHD patients with double-vessel and multi-vessel lesions (16.91±7.98 vs 18.39±7.78 μmol/L, P>0.05), but the two groups of patients had significantly lower plasma H₂S levels than patients with single-vessel involve- ment (33.04±15.01 μmol/L, P<0.05 and P<0.01, respectively). Plasma H₂S level was significantly lower in CHD patients with coronary artery occlusion than in patients with simple stenosis (19.04±9.55 vs 28.24±14.85 μmol/L, P<0.05). Among the CHD patients, H₂S levels were significantly lower in smokers than in non-smokers (27.54±10.37 vs 32.24±15.77 μmol/L, P<0.05), also lower in hypertensive patients than in normotensive patients (20.36±8.69 vs 33.77±15.86 μmol/L, P<0.01). Plasma H₂S levels showed a significant inverse correlation with blood glucose (r=-0.493 6, P=0.001 6), but there were no significant correlations with sex, age, cholesterol, triglyeride, TC, low-density lipoprotein, high-density lipoprotein, or body mass index. Conclusion Decreased plasma H₂S levels may correlate with the severity of CHD and changes of the coronary artery, and may implicate the risk factors of CHD such as smoking, hypertension, and high blood glucose.