BACKGROUND: Thrombolysis is a frontline treatment for stroke, which involves the application of tissue plasminogen activator (tPA) to trigger endogenous clot-degradation pathways. However, it is only effective within 4.5 h of symptom onset because of clot contraction preventing tPA permeation into the clot. Magnetic hyperthermia (MH) mediated by tumor-targeted magnetic nanoparticles is used to treat cancer by using local heat generation to trigger apoptosis of cancer cells. OBJECTIVES: To develop clot-targeting magnetic nanoparticles to deliver MH to the surface of human blood clots, and to assess whether this can improve the efficacy of thrombolysis of contracted blood clots. METHODS: Clot-targeting magnetic nanoparticles were developed by functionalizing iron oxide nanoparticles with an antibody recognizing activated integrin αIIbβ3 (PAC-1). The magnetic properties of the PAC-1-tagged magnetic nanoparticles were characterized and optimized to deliver clot-targeted MH. RESULTS: Clot-targeted MH increases the efficacy of tPA-mediated thrombolysis in contracted human blood clots, leading to a reduction in clot weight. MH increases the permeability of the clots to tPA, facilitating their breakdown. Scanning electron microscopy reveals that this effect is elicited through enhanced fibrin breakdown and triggering the disruption of red blood cells on the surface of the clot. Importantly, endothelial cells viability in a three-dimensional blood vessel model is unaffected by exposure to MH. CONCLUSIONS: This study demonstrates that clot-targeted MH can enhance the thrombolysis of contracted human blood clots and can be safely applied to enhance the timeframe in which thrombolysis is effective.