Thrombotic microangiopathies are characterized by platelet activation, 
endothelial damage, hemolysis and microvascular occlusion. This group of 
diseases is primary represented by thrombotic thrombocytopenic purpura (TTP) and 
hemolytic uremic syndrome (HUS). Patients present with microangiopathic 
hemolytic anemia and thrombocytopenia as well as occlusion-related organ 
ischemia to a variable degree. A deficiency of the metalloprotease ADAMTS-13 is 
a major risk for acute disease manifestation as this is a regulator of unusually 
large von Willebrand factor (vWF) multimers, which are extremely adhesive and 
secreted by endothelial cells. In classical TTP an ADAMTS-13 activity below 5% 
is specific, whereas in other forms of thrombotic microangiopathies activity of 
ADAMTS-13 ranges from very low to normal. Symptoms of different forms of 
thrombotic microangiopathy are frequently overlapping and a clear classification 
according to clinical criteria is often difficult. Due to a high mortality, 
particularly of TTP, immediate diagnosis and therapy are essential. In this 
article two cases of thombotic microangiopathy after cardiac surgery are 
reported. After exclusion of TTP and HUS as well as other etiologies of 
thrombotic microangiopathy a relationship between the use of extracorporeal 
circulation and the pathogenesis of thrombotic microangiopathy is assumed.