As mentioned above, both ACEi and ARB increase renin levels due to the loss of negative feedback of ANG II on renin release. Despite the aforementioned clues that high PRA might play a role in the progression of cardiac disease in patients on RAAS blockade, conclusive evidence is missing. Directly blocking the active site of renin may provide important information. It was already in 1980 that the first studies were performed with a renin inhibitor [78]; however, the effectiveness of this renin inhibitor was poor, mainly due to lack of specificity [79]. Recently, an orally active renin inhibitor, aliskiren, has become commercially available, and several other direct renin inhibitors are in development. Numerous studies are now trying to establish the potentials for this treatment in CV and renal disease. Despite low bioavailability, aliskiren blocks the active site of renin and effectively lowers PRA [80], thus providing very useful information on the role of PRA outside the classical RAAS pathway