Objective: To study the effect of Shenai injection (生脉注射液, SMI) on vascular endothelial and heart functions in coronary heart disease patients complicated with diabetes mellitus (CHD-DM). Methods: One hundred and twenty patients with CHD-DM, their diagnosis confirmed by coronary arteriography, were equally randomized into a control group treated with conventional treatment and a treated group treated with conventional treatment plus SMI. The changes in blood levels of nitric oxide (NO), endothelin-1 (ET-1) and angiotensin Ⅱ (Ang Ⅱ ), as well as endothelium-dependent vascular dilating function and heart function in the patients were observed before treatment and after the 3-week treatment. Results: After being treated with SMI for 3 weeks, in the treated group, blood level of NO was raised significantly from 69.8 ± 33.1 μ mol/L to 120.1 ± 50.8 μ mol/L, and ET-1 was lowered from 70.1 ± 32.1 ng/L to 46.2±21.3 ng/L, respectively (P<0.01); that of Ang Ⅱ was lowered from 81.3 ± 24.3 ng/L to 50.2 ± 27.3 ng/L (P<0.01); brachial arterial post-congestion blood flow increasing rate was raised from 389.4 ± 26.3% to 459.3 ± 27.8% (P<0.01); and the improvement in heart function as seen through the ejection fraction (EF) was increased from 44 ± 5% to 68 ± 6% (P<0.01), all the changes being more significant than those in the control group (all P<0.01). Conclusion: SMI can improve not only the endothelial function in CHD-DM patients, but also heart contraction significantly.