Oral anticoagulants have been used for over three decades in long-term post-myocardial infarction treatment. The cumulated results of the early clinical trials showed a reduction of general mortality of 20%. The reduction reached 60% when trials with adequate anti-coagulant treatment were considered. The most recent study (Sixty Plus Study 1980), a very well designed and conducted study with optimal anticoagulant dosage, reported a 2-year reduction in total mortality of 43% (p less than 0.017 vs. controls) and a reduction of reinfarction of 64.1% (p less than 0.0002). However, the incidence of major hemorrhagic episodes (27 vs. 3) and of definite intracranial hemorrhages (8 vs. 1) was very high in the treatment group with 6 deaths vs. 1 due to hemorrhage. An alternative way for controlling blood clotting activation and thrombin generation appears to be low-dose heparin treatment. In a randomized controlled clinical trial heparin administered in low doses (12,500 i.u. daily by subcutaneous route) reduced the reinfarction rate by 63% (p less than 0.05 vs. controls) and general mortality by 47% (p less than 0.05) over 2 years. Even the frequency of the fatalities attributable to thromboembolic events was significantly decreased. No hemorrhagic complication occurred in any patients. Oral anticoagulants and low-dose heparin appears to be equally effective in secondary prevention of myocardial infarction. However, low-dose heparin treatment appears to be free from the elevated risk of major hemorrhages related to oral anticoagulants and does not require any blood clotting check.