In 15 patients (group 1) with isolated mitral stenosis and in 14 patients (group 2) with isolated aortic stenosis the stenotic valve areas were calculated according to: A) Gorlin's formula; B) Hakki's simplified formula, using mean mitral gradient by planimetry or peak-to-peak aortic gradient; C) the three-point simplified formula, using mean gradient calculated by the three-point method for both mitral and aortic valve. The three-point method is definitely easier to use than planimetry. The values (mean +/- SD) of mitral valve areas in group 1 patients were, respectively: 1.56 +/- 0.63 cm2; 1.56 +/- 0.55; 1.51 +/- 0.53. The values of aortic valve areas in group 2 patients were: 0.91 +/- 0.63; 0.77 +/- 0.41; 0.88 +/- 0.52. An excellent correlation was shown between the valve area calculated by Gorlin's formula and both Hakki's simplified formula and the three-point simplified formula. For aortic valve area the correlation is even better if the mean gradient by the three-point method is used instead of the peak-to-peak gradient. On the basis of the simplified formula, a nomogram was constructed which allows an immediate calculation of valve areas from cardiac output and transvalvular gradient.