The hospital is one of the largest and most experienced centres in the world for heart and lung transplants. It has jointly pioneered work in the development of artificial hearts.The grounds of the hospital are also home to the Harefield Heart Science Centre, where much of the hospital’s pioneering research into the causes and treatments of heart disease is performed.

The hospital's most famous physician was the world famous Professor Sir Magdi Yacoub, who performed the first heart lung transplant in the world.

Harefield Hospital was known as Harefield Park before the 1st World War. It was owned by an Australian Millionaire Billyard-Leakes. In 1914 he was too old to join the army so he decided to help the war effort by offering his home and grounds as a field hospital for Anzac soldiers.

Many Anzac soldiers fought in the Turkish area in the Battle of Gallipoli.

The injured were brought back by boat to England and many came to Harefield. Many recovered and joined in with village activities.

In Christmas 1916 the children of the village were invited to a Christmas Party by the soldiers. Unfortunately not all the soldiers survived and the coffins were taken on a trolley down the hill to St. Mary's Church to be buried. The headmaster of the juniors gave the Union Jack to cover the coffin. As an act of gratitude the Australian government sent an Australian flag to the school. To this day, the children walk to the church on Anzac day to place flowers on the soldiers graves.