Background: Regarding the lower cost & availability of chest X-ray in comparison with echocardiography, cardiothoracic ratio (CTR) is used to estimate left ventricular ejection fraction (LVEF). Objective: To study CTR efficiency to estimate LVEF in Congestive Heart Failure (CHF) patients.Methods: In a one- year analytical study 96 CHF patients were examined consecutively at Qazvin Bou-Ali's hospital (1999-2000). CTR was measured by Danzer method & LVEF by Echo. Ischemic, hypertensive and dilated cases were accepted, whereas valvular diseases, corpolmonale, acute MI &persistent Arrythemia, were excluded.Findings: Correlation between CTR & LVEF was (r=-0.32) in all patients, and in subgroups was (-0.12) for ischemic, (-0.44) for Hypertensive, and (-0.49) for Dilated.Sensitivity & specifity of CTR in (0.5, 0.55 & 0.6) was calculated for Diagnosis of EF<40%.Conclusion: Direct measurement of EF by echocardiography is recommended for diagnosis, therapy & prognosis in CHF patients.