Thrombosis can be considered as inappropriate haemostasis. Platelets a
re involved in these two processes and also in atherogenesis. A recent
review (1) of hemorrheology, thrombogenesis and atherosclerosis discu
sses the effect of blood flow on the many factors in the blood stream
and vessel wall which may contribute to these multifactorial, clinical
entities, but platelets are hardly mentioned. However although an eff
ect of high shear forces on platelets has been known for some time (2,
3), only recently has the importance of shear been realised and explor
ed. A study of aortic valve stenosis has contributed a further underst
anding to this complex field. This article reviews relevant work and a
ttempts a synthesis of current knowledge in this field.