Cardiac alterations due to severe COVID-19 (referred to Werlein et al.⁸⁰). The figure panel was made by Christopher Werlein and Danny Jonigk, Institute of Pathology, Hannover Medical School, Germany and Institute of Pathology, RWTH University of Aachen, Germany. (A and B) Regular myocardium of the left ventricle. Cardiomyocytes (A) are arranged in regular fascicle with only sparse interstitial fibres. On immunofluorescence (CD68) only scarce macrophages in the interstitium are visible (B). (C–F) Left ventricular myocardium of a patient deceased from COVID-19. On light microscopy, no abundant changes are visible (C). On immunofluorescence (CD68), an increase in interstitial and especially perivascular macrophages are visible (D). Especially a distinct subpopulation of Tie2+ macrophages are more numerous and attaching to endothelial cells (CD31) (E). These macrophages supposedly increase a special form of neovascularization in COVID-19 hearts called intussusceptive neoangiogenesis that is visible on vascular corrosion casts of the capillary plexus by small holes (F). (A and C) hematoxylin-eosin staining, scale bar: 100 µm. (B and D) Immunofluorescence for CD68, scale bar: 100 µm. (E) Double-immunohistochemistry staining, scale bar: 20 µm.