Microvascular obstruction (MVO) remains a major unsolved clinical problem for optimal ST-elevation myocardial infarction (STEMI) therapy. Modern interventional STEMI therapy is both effective and efficient and rapidly restores epicardial flow to occluded coronary arteries. However, major adverse cardiac events (MACE) and other serious late complications are frequent after STEMI, most often resulting from distal MVO in dependent capillary beds. MVO occurs in 50% to 70% of STEMI patients (including those with Thrombolysis in Myocardial Infarction [TIMI] 3 flow), is difficult to detect in the cath lab, and has proven elusive to treat.