In a previous work based on popular belief,Campomanesia xanthocarpaBerg., popularly known as “guavirova”, showed to have a potential effect in the control of a number of conditions associated with cardiovascular diseases. The aim of the present work was to investigate the effects ofC.xanthocarpaextract (CXE) on antiplatelet, antithrombotic and fibrinolytic activities in mice and in human blood. Mice were treated orally for 5 days with CXE or acetylsalicylic acid and at the end of the treatment period animals were challenged for bleeding, acute thromboembolism and ulcerogenic activity. In addition, we have assessed the prothrombin time and activated partial thromboplastin time (aPTT) after oral administration. Inin vitroassays, antiplatelet effects of CXE was evaluated on platelet aggregation, and fibrinolytic activity of the extract was observed by mice or human artificial blood clot degradation. Platelet citotoxicity of the extract was also determined by the LDH assay. Results demonstrated that CXE has a significant protective effect on thrombosis. It also inhibits platelet aggregation without demonstrating cytotoxicity on platelets. CXE slightly prolonged aPTT and showed no ulcerogenic activity after oral administration. In addition, CXE showed a fibrinolytic activity. Thus,C.xanthocarpashowed antiplatelet, antithrombotic and fibrinolytic activities in mice.