Tissue Plasminogen Activator (tPA) is a medication that dissolves blood clots. tPA was approved by the FDA in 1996 to treat ischemic type strokes. About 8 out of 10 strokes are ischemic. tPA was approved to treat strokes in the first three hours following the onset of symptoms. If given promptly, 1 in 3 patients who receive tPA resolve their symptoms or have major improvement in their stroke symptoms. A recent large study showed that tPA remained beneficial even when it was given between 3 and 4.5 hours; in that study, 1 in 14 patients who received tPA resolved their symptoms fully. Unfortunately not everyone should receive tPA therapy. Persons who cannot be treated within 4.5 hours of their first symptom, patients with certain medical conditions, and patients with certain types of strokes will not qualify for this treatment.