A low cardiac output and high compliance of the systemic venous system may mask a resting tricuspid diastolic gradient in patients with significant rheumatic tricuspid stenosis. Thirty-three patients (mean age 28 +/- 10 years) with rheumatic tricuspid stenosis evidenced by 2-dimensional echocardiography (doming and restricted motion of all 3 tricuspid valve leaflets) were studied to expose occult and to amplify borderline and basal tricuspid valve gradients. At cardiac catheterization, the right atrium and right ventricular pressures were recorded simultaneously in the basal state, after intravenous infusion of 200, 400, 500, 700 or 1,000 ml of normal saline until a mean right atrial pressure of 12 mm Hg was achieved, and after 0.6 mg of intravenous atropine. Eleven patients (33%) had a mean tricuspid diastolic gradient of greater than 2 mm Hg at rest (group 1). After 483 +/- 240 ml of saline infusion, the mean tricuspid diastolic gradient increased from 5 +/- 2 to 9 +/- 3 mm Hg (p less than 0.001), secondary to a marked rise in right atrial pressure from 8 +/- 3 to 12 +/- 2 mm Hg (p less than 0.001). Concomitantly, there was no increase in right ventricular end-diastolic pressure, although the heart rate increased from 76 +/- 13 to 79 +/- 12 beats/min (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)