COVID-19 is a disease caused by a virus called SARS-CoV-2. Some people with COVID-19 develop abnormal blood clots, including lots of tiny clots in the smallest blood vessels. This video is by the National Heart, Lung, and Blood Institute (NHLBI), part of the National Institutes of Health (NIH). Learn more: https://www.nhlbi.nih.gov/coronavirus Follow us on Twitter: https://twitter.com/nih_nhlbi Like us on Facebook: https://www.facebook.com/NHLBI/