Background: Continuous effort is still provided in designing optimal artificial heart valves with better hemodynamic function and reduced thromboembolic potential. The question is do we have moved forward toward this goal or not. Methods: A prospective, randomized comparative study was done on 360 patients scheduled for elective mitral valve replacement. Patients were grouped into On-X group (n=180) who received On-X mechanical valve and SJM (n=180) who received St Jude mechanical valve. Echocardiographic and clinical assessments were performed for all patients at 6 and 12 months follow up period. Results: Rheumatic heart disease was the most common cause of valve affection (94.2%). Early mortality was 6.4%. The mean follow-up time was 3.11± 2.44 years. No structural or non- structural valvular dysfunction and no thromboembolism cases were encountered. Late valve thrombosis was1.9%/patient-year in On-X group and 2.1%/patient-year in SJM group. The mean EOA was higher in On-X group (2.0±0.3cm2) than in SJM group (1.9±0.2cm2), (P value ≥ 0.05). The mean EOAI was higher in On-X group (1.1±0.1cm2/m2) than in SJM group (1.0±0.1cm2/m2), (P value = 0.034), especially significant in small valve size (25mm) where it was 1.09±021cm2/m2 in On-X group and 0.93±0.12cm2/m2 in SJM group, (P value = 0.02). Conclusion: On-X and St Jude prosthetic valves have a comparable hemodynamic performance in mitral position. However, On-X prosthesis might have a forward step on the way of design technology that may allow better function in terms of EOA and EOAI especially in smaller valve size.