Chronic allograft vasculopathy (CAV) is a progressive disease of the small vessels that affects heart transplant patients and is a significant cause of morbidity and mortality. Traditional methods for diagnosing CAV rely on catheter based angiography and intravascular ultrasound (IVUS), which are both invasive and associated with potential adverse events. Stress perfusion cardiac MRI (CMR) is frequently used to noninvasively diagnose ischemic heart disease and has also been used to assess CAV in heart transplant patients. However, since CAV is primarily a disease of the microvasculature, sparing the larger more proximal epicardial coronary arteries, quantitative measures of myocardial perfusion may be more valuable than relying on subjective assessment alone.The purpose of this study was to evaluate semiquantitative measures of ischemia using noninvasive stress perfusion CMR in the detection of CAV using invasive coronary angiography as the standard reference.A cohort of 41 chronic heart transplant patients was studied using both stress CMR and coronary angiography. Stress CMR was performed in the standard manner using an IV injection of regadenoson and 0.2 mM/kg of an extracellular gadolinium based contrast agent. Based on the distribution of disease on the coronary angiogram, the patients were sub-divided into groups of no disease (group 1), mild chronic allograft vasculopathy (CAV) (group 2), and moderate to severe CAV (group 3), based on the International Heart Lung Transplantation (IHLT) guidelines for diagnosis of CAV. The time between the angiogram and perfusion results varied from less than 6 months to just over 2 years, with an average of about 1 year between studies. The rest and stress perfusion images were analyzed by segment based on the AHA 16 segment model of the heart using dedicated myocardial perfusion software (Argus, Siemens Healthcare). The upslope was measured for each segment on both stress and rest images. The myocardial perfusion reserve was calculated by dividing the upslope values of rest and stress images. The semiquantitative results of the perfusion studies, both stress perfusion upslope values and myocardial perfusion reserve, were then correlated to the angiogram results. Bullseye plots based on the 16 segment model were created and compared for each of the CAV groups.There were 18 patients with no evidence of CAV on angiography (group 1), 18 patients with mild CAV (group 2), and 5 patients with moderate to severe CAV (group 3). Both stress perfusion upslope and myocardial perfusion reserve tended to decrease with increasing disease severity (fig 1). This is exhibited in the bullseye plots (fig 2) by the decreasing average value as well as overall lower values for both stress upslope and myocardial perfusion reserve, demonstrated by an increase in dark red colored segments.Semiquantitative parameters of upslope and myocardial perfusion reserve as measured from stress perfusion CMR can detect both mild and moderate to severe CAV in heart transplant patients. Stress perfusion CMR is a promising noninvasive tool for detecting CAV potentially obviating the need for regular invasive coronary angiography.