More than five decades after the first human-to-human heart transplant, over 5,000 heart transplants are performed annually worldwide. However, this number falls significantly short of meeting the demand, as up to 50,000 individuals may require a transplant at any given moment. The wait time for a transplant can span years, influenced by the severity of the patient’s condition as well as various physiological and logistical factors. A major limitation in meeting this need is the scarcity of suitable donor hearts, partly due to the very short time window for transplantation once the heart is removed from the deceased donor.

The current ‘gold standard’ for preserving donor hearts is cold static storage (CSS), where hearts are kept on ice until transplantation. Transplantation is most successful when CSS lasts less than six hours, before the heart or its blood vessels undergo damage. Periods up to 12 hours are sometimes possible, but require mechanical life support such as extracorporeal membrane oxygenation (ECMO) for several days on the recipient. Prolonging the storage period beyond six hours without the need for ECMO would thus be a medical breakthrough.