Tissue plasminogen activator: (tPA) An enzyme that helps dissolve clots. tPA is made by the cells lining blood vessels and has also been made in the laboratory. It is systemic thrombolytic (clot-busting) agent and is used in the treatment of heart attack and stroke. Activase (alteplase) is a tissue plasminogen activator produced by recombinant DNA technology. Recombinant tPA is abbreviated r-tPA.