Abstract： Objective To investigate the prevalence and the characteristics of heart failure (HF) in medical intensive care unit (ICU) so as to explore the factors contributing to HF. Methods A retrospective analysis of the data of HF was carried out in 887 HF patients (54. 2％ ) males; age (69.83± 13.57) years oldadmitted to the medical ICU from October 2006 through June 2010. Clinical variables were systematically reviewed for all enrolled patients. HF as either major or additional diagnosis was recorded and the potential risk factors for HF were explored. Left ventricular systolic function was evaluated in HF patients by using ejection fraction (EF) measured by echocardiography. Multivariate Logistic regression analysis was used to identify the independent factors contributing to HF in medical ICU patients. Results Of the 887 patients, 74. 1％ aged 65 years or over, and 53％ had organ dysfunction. The prevalence of HF in medical ICU patients was 22. 8％. Echocardiography measurement revealed that left ventricular systolic function was preserved in 62. 5％ of HF patients with an EF ＞ 50％. Underlying heart diseases were identified in 72. 8％ of the HF patients, and coronary artery disease accounted for the vast majority (52. 5％ ), followed by valvular heart disease ( 17. 8％ ). Structural heart diseases were not identified in 27. 2％ of the HF patients. 4) After the adjustment of age and gender, multivariate regression analysis showed that coronary artery disease ( OR =7. 364, 95％ CI: 4. 979 ～ 10. 890, P ＜0. 01 ), valvular heart disease ( OR =18. 023, 95％ CI: 9. 280 ～ 35. 002, P ＜ 0. 01 ), diabetes mellitus ( OR =2. 154, 95％ CI: 1. 227 ～ 3. 784, P =0. 0076), respiratory failure ( ( OR =1. 527, 95％ CI: 1. 045 ～ 2. 229, P =0. 0285 ), and renal dysfunction ( OR =2. 638, 95％ CI: 1. 621 ～ 4. 294, P =0. 0001 ) were associated with risk increased for HF in medical ICU. Conclusions HF is highly prevalent in medical ICU and its etiology is multi-factorial. The high rate of HF with preserved EF highlights the importance of enhanced alertness for HF with preserved systolic function in ICU.