NPPA and heart failure: However, the discovery of the novel MRproANP fragment [42], a substantially more stable peptide compared to N-ANP and ANP [43] due to the assay epitopes being located internally on the proANP molecule (and hence stability to exoprotease activity), has led to the finding that MRproANP is at least as good at predicting death and heart failure as NTproBNP [44].