Systems and apparatus are included that are configured to determine the effectiveness of apparatus and methods used to diagnose and unblock microvascular obstruction (MVO). An infusion system blocks antegrade flow for a short time and measures vascular pressure response as an infusate is infused in stepwise fashion at increasingly higher flowrates. During the antegrade flow occlusion, calculations of the real-time vascular resistance can be obtained using the formula R(t)= P(t)/Q
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