ACE and heart failure: The resulting radiotracer proved to be a valuable tool for the in vitro quantification of ACE levels in tissue samples from ischemic cardiomyopathy and patients with heart failure [20] [99mTc]Tc-tricarbonyl-based lisinopril radiotracers investigated for preclinical imaging of ACE in normal and transgenic rats for human ACE showed, however, substantial hepatobiliary excretion with high background accumulation in the liver and intestinal tract [16, 22].