How the EROA (PISA) Calculation Works
Effective regurgitant orifice area (EROA) is a quantitative echocardiographic measure of how large the "leak" is at a regurgitant heart valve, most commonly the mitral valve. It is derived using the Proximal Isovelocity Surface Area (PISA), or flow-convergence, method: as blood accelerates toward a regurgitant orifice, it forms a series of hemispheric shells of increasing velocity. Color Doppler is used to identify the radius (r) of the hemisphere where flow velocity equals a chosen aliasing velocity (the Nyquist limit shown on the color scale). Because flow rate is conserved across that hemisphere, the instantaneous regurgitant flow rate equals the surface area of the hemisphere multiplied by the aliasing velocity: Flow rate (mL/s) = 2π × r² × Va. Dividing that flow rate by the peak velocity of the regurgitant jet (measured with continuous-wave, or CW, Doppler) gives the EROA: EROA (cm²) = Flow rate ÷ Peak jet velocity. Multiplying EROA by the velocity-time integral (VTI) of the same CW Doppler jet gives the regurgitant volume ejected per beat: RVol (mL) = EROA × VTI.
Entering the right measurements
All four inputs come directly off the echocardiogram: the PISA radius (r) is measured from the color Doppler flow-convergence image, in centimeters; the aliasing velocity is the Nyquist limit (the velocity at the color transition) set on the machine at the time the radius was measured, in cm/s; the peak jet velocity is the maximum velocity traced on the CW Doppler spectrum of the regurgitant jet, in m/s (the calculator converts this to cm/s internally); and the VTI is the area traced under that same CW Doppler envelope, in cm. Because EROA is sensitive to the aliasing velocity chosen and to accurate radius measurement, small measurement errors can meaningfully shift the calculated area — this is a known limitation of the PISA technique, not a flaw in the arithmetic.
Interpreting severity
The American Society of Echocardiography (ASE) guidelines for quantifying primary (degenerative) mitral regurgitation classify severity using both EROA and regurgitant volume: mild is EROA under 0.20 cm² and RVol under 30 mL; moderate is EROA 0.20-0.39 cm² and RVol 30-59 mL; severe is EROA 0.40 cm² or higher and RVol 60 mL or more. These thresholds are intended to be used together with other echocardiographic findings (jet area, vena contracta, pulmonary vein flow pattern) and the clinical picture — a single PISA measurement should never be the sole basis for a treatment decision. This calculator is an educational and reference tool for understanding the PISA method; it is not a diagnostic device, and results should always be reviewed with a cardiologist alongside the full echocardiographic study.