The investigators will use cardiac MRI to measure the myocardial perfusion reserve and amount of myocardial edema and fibrosis in heart-transplant patients with nonspecific allograft dysfunction in contrast to those with normal graft function. The investigators hypothesize that patients with nonspecific allograft dysfunction will demonstrate decreased myocardial perfusion reserve, related to microvascular allograft vasculopathy, compared to those with normal graft function.