Background: Cardiac functioning and assessment in patients with established CAD can be done through performing Echocardiography and calculating the Ejection Fraction, which is an important and vital tool in clinical practice and related to prognosis. Left Ventricular Ejection Fraction (LVEF) can predict future clinical outcome and assist in risk stratification. Objective: The aim of this research was to evaluate the relationship between lower EF with clinical and biochemical markers, and to determine the predictors of left ventricular EF in patients with established CAD whose younger than 35 years’ age. Patients and Methods: This study was enrolled in Surgical Specialty Hospital- Cardiac Center / Erbil-Iraq among 100 consecutive patients (77 males and 23 females) between November 2016 to December 2017 of those whose age was ≤ 35 years old. Results: The mean age was 31.6 ± 2.91 years with an Age range of 24-35 years. 22.9% of those with Anterior Wall Myocardial Infarction (AWMI) and 22.7% of those with Inferior Wall Myocardial Infarction (IWMI) had left ventricular Ejection fraction (LVEF) of less than 44% (P = 0.0001). 33.3% of Patients with STEMI on presentation, later had LVEF of ≤ 44% (P = 0.0001). Lower LVEF (≤44%) was observed more in male gender and smoker patients with established CAD (P <0.05). 29% of those with 10-fold S. Troponin level elevation on presentation, had LVEF ≤44% and 45.2% of them had LVEF of between 45%-54% (P =0.001). 37.5% of those with Very High LDL levels had EF ≤44% (P = 0.02). After performing Coronary Angiography, 68.8% of those with poor functioning of heart (LVEF ≤ 44%) had LAD lesion. (P < 0.05). Conclusion: We concluded that there was evidence of a strong relationship (Inversely Proportional) between Poor EF with high LDL and Markedly Elevated Serum Troponin of more than 10 folds, young Patients with AWMI and IWMI had Poor functioning of the heart. (LVEF of ≤44).