In recent years coronary artery bypass grafting (CABG) has been extended to include patients with very low left ventricular ejection fractions (LVEF), also frequently with co-existing mild to moderate mitral valve regurgitation (MR). The question is, should such a MR be corrected simultaneously with a myocardial revascularization or not? Between January 1989 and November 1994, 56 patients with preoperative LVEF < or = 25% and echocardiographic evidence of co-existing MR (Grade I: 41%, II: 46%, III: 13%) underwent primary CABG. None of them had simultaneous mitral valve surgery. Twenty-nine patients (52%) had a pulmonary artery pressure (PAP) > 40 mmHg. The mean preoperative LVEF was 17.9 +/- 4.6 (10-25), mean PAP 44.2 +/- 16.1 mmHg. An average of 4.5 +/- 1.5 grafts/patient were placed and five patients had simultaneous repair of a post-infarction left ventricular aneurysm. The overall mortality was 3.6% (2/56). Transient post-operative low cardiac output syndrome occurred in 16 patients (29%). Twenty-one patients (38%) had no postoperative complications at all. The 54 hospital survivors were followed up over a mean period of 12 months (3-36 months). There was one death (eight months postoperatively) and two graft occlusions, not requiring reoperation. At the end of the follow up echocardiography showed that 50 patients (93%) had no (31 patients) or only a very mild Grade I MR (19 patients). Four patients had Grade II MR, none of them requiring mitral valve surgery. All patients improved their NYHA functional class, from 3.4 +/- 0.8 to 1.9 +/- 0.7 and LVEF from 17.9 +/- 4.6 to 44.2 +/- 7.4 (p < 0.001). Coronary artery bypass grafting is a possible treatment for patients with very low LVEF, provided the patient has a two- or three-vessel disease with significant coronary artery stenosis (> 70%) and angina. Mortality and morbidity are low. Moderate co-existing MR (Grade I-III) seems to normalize after myocardial revascularization and should not be surgically corrected therefore at the primary operation.