We have simplified the Gorlin formula and have compared our measurements of the aortic or mitral valve area, using the original Gorlin formula and the simplified valve formula in 100 consecutive patients. The valve area was measured by the simplified formula as cardiac output (l/min) divided by the square root of pressure differences across the valve. In patients with aortic stenosis of varying severity there were excellent correlation between the original Gorlin formula and the simplified formula (r = 0.96, y = 0.99x + 0.01, SEE = +/- 0.10, p less than 0.001). The correlation was unchanged when the peak gradient was used instead of the mean gradient in the simplified formula. Excellent correlation was also seen in patients with mitral stenosis of varying severity (r = 0.94, y = 0.97x - 0.02, SEE = +/- 0.19; p less than 0.001). The simplicity of the formula makes it easy to memorize and use.