Endomyocardial biopsy (EMB) is the gold standard method to guide post-heart trasplant (HT) patients, as it represents the best tool to identify rejection in orthotopic HT. However, it is frequently repeated during the first year, with some variations depending on each center protocol and it is potentially associated with serious complications.Several studies have presented the association between acute allograft rejection, micro-vasculopathy and cardiac allograft epicardial vasculopathy (CAV). Index of microvascular resistance (IMR) measured early after HT has been significantly associated with the risk of acute cellular rejection (ACR). The aim of this study will be to evaluate if the use of IMR early after HT may improve the patients care after HT, by reducing the number of EMB.