Full recovery of donor heart function often takes place over hours or days, during which time considerable damage can occur. Other deaths to patients can occur from preexisting conditions. For example, in pulmonary hypertension the patient's right ventricle has often adapted to the higher pressure over time and, although diseased and hypertrophied, is often capable of maintaining circulation to the lungs. Barnard designed the idea of the heterotopic (or "piggy back" transplant) in which the patient's diseased heart is left in place while the donor heart is added, essentially forming a "double heart". Barnard performed the first such heterotopic heart transplant in 1974.