The purpose of this study is to demonstrate superiority on postoperative bleeding from the use of a heparin half dose compared to a conventional dose, under mini-extra corporeal circulation, without increased risk to the patient.

Usually management of conventional extra corporeal circulation takes place under a loading heparin dose of 300 IU / kg to achieve an ACT (activating clotting time) target more than 400 seconds. This empirical approach based on patient weight date from the 1960's and does not take into account materials improvement and different individual sensitivities; several studies have demonstrated than a result at least as effective could be obtained with heparin lower doses, and without increasing thromboembolic morbid events for patients.

Patients are randomly assigned into one of 2 groups one day before surgery. First group receive unfractionated heparin conventional dose during the MECC, second group receive half of the conventional dose. All surgery is performed by the same team and using same equipment. Regular blood tests are carried out before, during and after surgery. Blood loss, transfusion needs, rhythm disorders, stay duration in intensive care and total hospitalization length is finally reported. The follow-up period through the 30th postoperative day.

Inclusion Criteria:

• single or multiple coronary bypass
• written and informed consent
• repair or replacement of artic leaflet
• platelet suppressive agents stopped since at least 7 days
• anticoagulants stopped since at least 3 days

Exclusion Criteria:

• Thoracic surgery antecedent
• ASA 4
• carotid stenosis > 75%
• Hb < 10,5 g/l
• chronic hepatic failure
• thromboembolic antecedent