['With regard to a deficiency in atrial natriuretic peptide (ANP) secretion, the relationship between plasma ANP and left atrial diameter measured by echocardiography was examined and the efficacy of postoperative supplementation was evaluated.', '(1) Ninety-six patients with mitral valve disease from 1997 to 2002 (M:F = 65:31, mean-age 65.3 +/- 8.9 years) were studied for relationship analyses. (2) Twenty-six patients with mitral stenosis and left atrial diameter > or = 60 mm undergoing mitral valve replacement (M:F = 17:9, mean-age 67.4 +/- 7.5 years) were randomly allocated to one of two groups; ANP-treated group (n = 13, 0.05 microg/kg/min of synthetic human alpha-ANP was postoperatively administered) and Control group (n = 13).', '(1) There were significant positive correlations between left atrial diameter and plasma renin-activity (r = 0.690, P < 0.01) and between left atrial diameter and plasma aldosterone (r = 0.757, P < 0.01). The maximum value of plasma ANP was 249.5 pg/mL accompanied with 56.2 mm of left atrial diameter in 29 patients suffering from mitral stenosis. There was a significant negative correlation between left atrial diameter and ANP in patients with left atrial diameter > 56.2 mm (r = - 0.725, P < 0.0001), whereas there was a significant positive correlation in patients with left atrial diameter < or = 56.2 mm (r = 0.529, P = 0.0066). (2) At 24 hours after operation, the ANP-treated group showed significantly lower plasma renin-activity (9.2 +/- 3.3 versus 36.2 +/- 7.4 ng/mL/h) and aldosterone (113.6 +/- 36.9 versus 473.8 +/- 95.8 pg/mL) than the Control group.'] Is left atrial diameter a simple indicator of a deficiency in atrial natriuretic peptide secretion in patients with mitral stenosis : efficacy of postoperative supplementation with synthetic human alpha-atrial natriuretic peptide?