Our research is based on the critical evaluation of plasma concentration variation of B-type natriuretic peptide (BNP)--in emergency--in paroxysmal atrial fibrillation, acute pulmonary edema, acute coronary syndrome and dilated cardiomyopathy. The aim of our research was to assess if the BNP concentration variation may be useful in the diagnosis and therapy. Peptide synthesis takes place mainly in the ventricular myocardium. We selected 102 patients: 27 control subjects, and 75 admitted to the emergency and reception department for dyspnea and/or precordialgia and/or palpitations. At the beginning they were considered as one group only, and then they were divided into groups according to the diagnosis: 20 with paroxysmal atrial fibrillation with reversion to sinus rhythm in the first week; 20 with acute pulmonary edema; 22 with acute coronary syndrome without electrocardiographic ST-segment changes; 13 with compensated dilated cardiomyopathy. Our research assessed that the BNP activation and secretion are evident especially in patients with heart failure and remains at the high level until the administration of an effective therapy and then they reach a balance with values higher than the standards, while in the paroxysmal atrial fibrillation and in acute coronary syndrome they rise and come back to the standard levels or even at lower levels after the disease solution. For this reason, BNP reiterated measurements allow to assess treatment efficacy, even at home, and to optimize the therapy. The main limit of BNP diagnostic role is in the need of knowing in advance the specific values for each patient. The BNP concentration evaluation in the acute phase is necessary to differentiate patients with dyspnea due to heart failure from those with pulmonary pathologies, while the BNP assessment in the acute coronary syndrome predicted exitus or heart failure manifestations.