Cardiac PDGFR binding density and subtypes: As detected by quantitative in vitro autoradiography, PDGFR was observed in the normal myocardium (panel A). Following MI, PDGFR levels were increased in the infarcted myocardium at day 3 (panel B) and remained elevated at day 7, 14, 28, and 42 (panels C–F). PDGFR in the noninfarcted myocardium remained unchanged at day 3 and 7 and then increased from day 14 to 42. PDGFR binding was partially displaced by PDGF-AA in the control (panel G) and infarcted heart (panel H).