Therapeutical trials in the acute phase of stroke have showed a moderate benefit of administration of aspirin in prevention of death or recurrent cerebral events. This benefit was obtained despite a small increase in systemic and cerebral haemorrhages. Heparin used at high dosage, without any control of coagulation test, induces an excess of cerebral and systemic haemorrhage which overset its benefit in prevention of recurrent cerebral events. Similar results have been observed with heparinoid and nadroparine used at high dosage. The only benefit of anticoagulation is the prevention of total and fatal pulmonary embolism which has been observed in all recent studies. The antithrombotic treatment which offers the best ratio benefit-risk in the acute phase of stroke is aspirin at a minimum dosage of 160 mg by day and, if risk factors are present, heparin at an adequate dosage to prevent venous thrombo-embolism. Explicative studies are required to explore the potential benefit of heparin in patients with a high risk of recurrent cerebral ischemic events.