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The present study analyzes the hemodynamics of intracardiac occlusive priods during balloon mitral or aortic valvuloplasty and compares them with immediate plasma levels of atrial natriuretic factor (ANF), vasopressin and renin activity. Forty-nine patients were studied; 33 of them had mitral stenosis and 16 had aortic stenosis. The mean age was 52 [+ or -] 17 years. During dilations pressures were monitored from the ascending aorta and left atrium. Plasma levels of ANF, vasopressin and renin were serially determined at baseline, after diagnostic procedures, within 15 to 30 seconds after the first 2 occlusive dilations, and 1 and 7 hours later. There were no significant changes in plasma renin throughout the study stages. ANF and vasopressin significantly increased after the dilations. These hormonal changes were related to the significant hemodynamic changes observed during intracardiac occlusion. The left atrial pressure correlated directly and significantly (r = 0.54, p [is less than]0.001) with plasma ANF levels throughout the conditions. On the other hand, the plasma vasopressin also correlated (r = 0.76, p [is less than]0.001) with systemic pressure in an exponential fashion. These findings show that abrupt releases of ANF and vasopressin occur immediately after intracardiac occlusive periods as a response to the acute and transient hemodynamic changes observed., Homeostatic response refers to the adjustment of the body to maintain equilibrium which is sustained via feedback and regulation mechanisms. A study of the response to abrupt physiological changes was performed by the measurement of plasma levels of atrial natriuretic factor (ANF), vasopressin and renin activity prior to and at intervals after balloon valvuloplasty was performed on 49 patients. These three hormones are involved in the control of blood pressure by their effect on the blood vessels. Thirty-three patients had stenosis (narrowing or closing) of the mitral valve in the heart and 16 had stenosis of the aorta, the main arterial vessel leading from the heart. Balloon angioplasty involves the insertion of a tube with a small balloon at its end into the artery; the balloon is inflated at the point of closure to open the vessel and increase blood flow. Dilations were monitored from the ascending aorta and from the left atrium. Baseline blood level measurements of the hormones were first taken at 15 to 30 seconds after the procedure and again at one to seven hours after the procedure, and were then plotted against systemic blood pressure. Changes in concentrations of these hormones were observed to correlate with changes in blood flow produced by the angioplasty; abrupt release of ANF and vasopressin occurred. Increase in ANF was found to be proportional and elevated vasopressin concentrations correlated exponentially. No change in renin levels was recorded. The effect of vasopressin release may provide rapid control of arterial pressure and thus account for the patients' good general tolerance of the balloon valvuloplasty. However, the release of higher concentrations of ANF would likely counteract the effects of vasopressin. The benefits and the apparent contradictory behavior of these mechanisms need to be better understood and further research is recommended.