The aim of this paper is to present an evidence that ABO blood-groups play a key role in the rheology of blood in cardiovascular diseases, that they might influence the pathways of aetiology of these diseases, especially in relation to the microcirculation, tissue perfusion and thrombus formation, and that there exists a possibility that ABO blood-group specific drugs might be more effective in counteracting a development and progress of these diseases than drugs which do not take any account of inherent differences between patients of different ABO blood groups. ' ' ' BACKGROUND