miRNA is released from activated platelets. (A) Platelet miRNA levels in patients with STEMI (n = 10) and control patients (n = 15) are expressed relative to U6 small nuclear RNA and normalized to the mean of the control samples. **P < .01; ***P < .001. (B) miRNA levels in the supernatant of pelleted platelets from 3 individual donors before and after aggregation with 1 U/mL thrombin (n = 3). Data are expressed relative to an exogenous RNA spike-in and normalized against the control samples (before aggregation). (C) Levels of miR-22, -185, -320b, and -423-5p in platelets of healthy individuals (n = 15), patients with STEMI (n = 10), and thrombi aspirated from patients with STEMI (n = 2) relative to U6 RNA. N.D. indicates not detected.