Background: Ischemic heart disease, also called coronary artery disease, is the term given to heart problems caused by narrowed heart (coronary) arteries that supply blood to the heart muscle. Aim of the Study: The aim of the study is to determine the levels of Nitric oxide synthase (eNOS) in patients with coronary artery disease. Patients and Methods: The current study is case-control study conducted in Tikrit city during the period between 10th of January to 10th of April 2023 on patients admitted to Coronary Care Unit of Salah Al-Din Teaching Hospital The study included 60 Iraqi patients with coronary heart disease with age range (37-66 years). The study also included 30 healthy individuals with same age range and from both sexes who apparently haven’t any acute or chronic diseases. Blood was collected from each patients for determination Nitric oxide synthase by enzyme-linked immunosorbent assay (ELISA) and lactate dehydrogenase (LDH) by chemiluminence technique. Results: The study showed that lowest mean of Human Endothelial Nitric Oxide Synthase (eNOS) was detected among IHD patients (2.41±0.74 ng/ml) and the maximum mean was within the control group (5.15±1.24 ng/ml). The differences were highly significant (P-value: 0.0001). The study confirmed that the peak mean of lactate dehydrogenase was detected among IHD patients (257.8±94.9 IU/L) and the deepest mean was in the control group (168.9±16.8 IU/L). The differences were highly significant (P-value: 0.0001). The study showed that the mean eNOS was 2.17 ng/ml in patients with hypertension, which was significantly lower than that in non-hypertensive IHD patients (2.76 ng/ml), at a P value of 0.024. The study showed that the mean LDH was 284.6 IU/L in patients with hypertension, which was significantly more than that in non-hypertensive IHD patients (217.5 IU/L), at a P value of 0.001. Conclusions: In conclusion, the findings of the study suggest that patients with ischemic heart disease (IHD) have reduced levels of serum eNOS compared to healthy individuals. More researches are needed to fully understand the relationship among eNOS, cardiovascular disease and to determine the clinical utility of their measuring in the diagnosis and management of these conditions.