An increased level of N-terminal pro-B-type natriuretic peptide (NT-proBNP) represents an established hallmark in patients with HF, however, this biomarker is markedly influenced by the presence of concomitant AF, making it difficult to distinguish between HF versus AF as the primary determinant of a raised NT-proBNP. The gene discussed is NPPB; the disease is atrial fibrillation.