Human endothelium tissue samples are specimens containing endothelial cells, which form the inner lining of blood vessels within the lung tissue. Endothelial cells play a vital role in regulating vascular tone, blood clotting, inflammation, and angiogenesis. These samples are critical for studying vascular diseases within the lung, such as pulmonary hypertension, and for understanding the interplay between the vasculature and respiratory pathologies. Researchers use these tissues to investigate endothelial dysfunction, vascular remodeling, and the effects of various factors on pulmonary circulation. Samples can be provided as sections from fixed tissue in paraffin blocks or OCT, or as snapfrosts of fresh tissues.