Conventional EM and immuno-EM were combined and applied to study cardiac tissue samples from dilated cardiomyopathy (DCM) patients with atrioventricular block (AVB) caused by mutations in LMNA. Electron microscopy allowed Verga and coworkers [15] to discover that nuclei of cardiomyocytes (CMs) from patients carrying LMNA mutations display an irregular shape. The gene discussed is LMNA; the disease is atrioventricular block.