Thrombolytic therapy is a treatment used to break up dangerous clots inside your blood vessels. To perform this treatment, your physician injects clot-dissolving medications into a blood vessel. In some cases, the medications flow through your bloodstream to the clot. In other cases, your physician guides a long, thin tube, called a catheter, through your blood vessels to the area of the clot. Depending on the circumstances, the tip of the catheter may carry special attachments that break up clots. The catheter then delivers medications or mechanically breaks up the clot.

Thrombolytic therapy commonly is used to treat an ischemic stroke, which is another name for a clot in a blood vessel in your brain. It can also be used to treat clots in:

A lung artery, called a pulmonary embolism;

The deep veins of your leg, called deep vein thrombosis (DVT);

Your heart, which may cause a heart attack;

An artery elsewhere in your body, such as in an arm or leg artery; or

A bypass graft or dialysis catheter that has become blocked.

From http://www.vascularweb.org/patients/NorthPoint/Thrombolytic_Therapy.html