When was the first successful blood transfusion performed?

James Blundell performed the first recorded successful human-to-human blood transfusion in 1818 in London. He used the procedure to treat women suffering from severe postpartum hemorrhage. At the time, doctors did not yet understand blood groups, so transfusions were risky and often unsuccessful. The breakthrough helped lay the groundwork for modern transfusion medicine, which became much safer after blood groups were discovered in the early 20th century.