Atrial fibrillation reduces the specificity of the NT-proBNP biomarker in the diagnosis of heart failure. NT-proBNP is elevated in patients with atrial fibrillation even in the absence of heart failure. This means that high NT-proBNP does not always mean heart failure if atrial fibrillation is present. Therefore, it is necessary to adjust the threshold values of NT-proBNP and supplement the examination with echocardiography. Modified approaches help maintain the high negative predictive value of the test in primary care. The results of the study show that NT-proBNP remains a useful tool, but its interpretation requires consideration of atrial fibrillation.