The Female Lead Has Heart Disease That Nobody Around Her Knows About, and Returns Years Later, Cured

The heroine transfers to a high school, and nobody around her knows she has a heart condition. After an accident, she gets injured and her condition flares up, so she has no choice but to go abroad for treatment. The hero knows and falls into a deep slump, but soon pulls himself together and focuses on his studies. A few years later, the heroine returns after recovering.