Heart transplantation is an effective life-saving treatment for patients with end-stage heart disease. After a transplant, the new heart may develop narrowing in the arteries, causing heart failure, heart attacks and abnormal heart rhythms. This condition is known as cardiac allograft vasculopathy (CAV). The disease is very common, affecting almost a third of heart transplant patients by 5 years after transplant. CAV is a serious problem that causes the new heart to fail and is one of the main causes of death after transplant. Early detection of CAV is important as treatment options are poor once the disease is established. Currently, available techniques to evaluate CAV are limited by poor ability to detect disease early. The current tests usually focus on the large heart arteries and do not examine the smaller arteries that are also affected.