Publisher Summary Thrombolytic drugs and heparin affects the blood coagulation and their actions have been reported in this chapter. There is considerable confusion around the heparin-platelet interactions often lumped together as heparin-induced thrombocytopenia. Hypersensitivity reactions to unfractionated or low-molecular weight heparin are reported; they may induce a global cardiovascular collapse or be limited to necrosis of the skin overlying the injection sites or cause distant cutaneous necrosis, without any site of predilection. Large hematomas of the abdominal wall can even occur after low dose calcium heparin and become a life threatening complication. In addition to its anticoagulant effect, heparin releases lipoprotein lipase from adipose tissue and skeletal muscle. The resultant lipoprotein lipase catabolism of serum lipoproteins yields lipid remnants that are processed rapidly by the liver and at extrahepatic sites. Heparin is also supposed to cause depression.