The aim of the present study was to determine whether oral pretreatment with micronized purified flavonoid fraction (Daflon) has beneficial effects on cardiac function and outcome after cardiac operations. This prospective, randomized trial enrolled 43 patients who had an impaired preoperative left ventricular ejection fraction of less than 0.50 (mean, 0.45 +/- 0.04) and a mean New York Heart Association functional class status of 2.30 +/- 0.74; all were scheduled for elective coronary artery bypass grafting. Patients who were randomized to the Daflon group (n=21) received oral Daflon 500 mg (6 tablets daily for 4 days, followed by 2 tablets for 3 days) preoperatively. Outcome variables included perioperative hemodynamic data, inotropic requirements, morbidity, and death, as well as cardiac ischemia and various outcome markers. Hemodynamic and biochemical data were collected before induction of anesthesia, perioperatively before starting cardiopulmonary bypass, immediately after bypass, and at the 24th postoperative hour. There was only 1 death (in the Daflon group). During the post-cardiopulmonary bypass period, troponin I and lactate dehydrogenase levels were significantly lower in the Daflon group. Also, the New York Heart Association status of the patients in the Daflon group was significantly lower postoperatively. Differences between the 2 groups in lengths of stay in the intensive care unit and hospital, inotropic requirements, and left ventricular ejection fraction levels did not reach statistical significance. Orally administered Daflon might provide better outcomes for patients who have impaired cardiac function before undergoing cardiac operations that require cardiopulmonary bypass.