['The purpose of this study was to investigate whether atrial and brain natriuretic peptides (ANP and BNP, respectively) represent autocrine/paracrine factors and are accumulated in pericardial fluid.', 'ANP and BNP, systemic hormones produced by the heart, have elevated circulating levels in patients with heart failure. Recent evidence suggests that the heart itself is one of the target organs for these peptides.', 'With an immunoreactive radiometric assay, we measured the concentrations of these peptides in plasma and pericardial fluid simultaneously in 28 patients during coronary artery bypass graft surgery.', 'The pericardial levels of BNP were markedly elevated in patients with impaired left ventricular function. We investigated the correlation of ANP and BNP levels in plasma or pericardial fluid with left ventricular hemodynamic variables. None of the hemodynamic variables correlated with ANP levels in plasma or pericardial fluid. Both plasma and pericardial fluid levels of BNP were significantly related to left ventricular end-diastolic and systolic volume indexes (LVEDVI and LVESVI, respectively). In addition, BNP pericardial fluid levels had closer relations with LVEDVI (r = 0.679, p < 0.0001) and LVESVI (r = 0.686, p < 0.0001) than did BNP plasma levels (LVEDVI: r = 0.567, p = 0.0017; LVESVI: r = 0.607, p = 0.0010). BNP levels in pericardial fluid but not in plasma correlated with left ventricular end-diastolic pressure (r = 0.495, p = 0.0074).'] Is marked elevation of brain natriuretic peptide levels in pericardial fluid closely associated with left ventricular dysfunction?