Complex sentence: After medical school Valantine performed post-graduate work in cardiology at the Brompton Hospital and Hammersmith Hospital in London before becoming a fellow at Stanford, where she worked with Norman Shumway, an early pioneer in the field of heart transplants.
Split into simpler sentences: After medical school Valantine performed post-graduate work in cardiology at the Brompton Hospital and Hammersmith Hospital in London. After her residencies in the UK, she became a fellow at Stanford, where she worked with Norman Shumway, a major early contributor to the field of heart transplants.