Fibrinolysis leads to the breakdown of fibrin clots ( blood clots ) and is caused by the action of several enzymes. Fibrinolysis normally occurs continuously to keep naturally occuring blood clots from growing and causing problems. However, fibrinolysis can increase under certain conditions (such as intense exercise , inadequate oxygenation of tissues, low blood sugar , or bacterial infections). Primary fibrinolysis refers to the normal breakdown of clots, whereas secondary fibrinolysis is the breakdown of blood clots and possible abnormal bleeding due to another medical disorder, medications, or other causes. In some situations, doctors may wish to speed up the rate of fibrinolysis. For example, when an abnormal "clot" forms in the blood vessels of the heart and results in a heart attack, man-made fibrinolytic enzymes (such as tPA, streptokinase, or Retavase) may be given to break up the culprit clot.