Enter the cardiac output, heart rate, systolic ejection period, and mean gradient (Main tab) into the calculator to determine the effective orifice area.

Effective Orifice Area Calculator

Main: Aortic (Gorlin-style, SEP)
Gorlin (Cath) Valve Area
Continuity Equation (Echo)

Main tab uses a Gorlin-style relationship with systolic ejection period (SEP). Enter any 4 values to calculate the missing variable.







Medical disclaimer: For informational use only—not medical advice and not a diagnosis. Valve stenosis severity requires clinician interpretation using multiple measurements (e.g., symptoms, gradients/velocities, flow state, and imaging quality). If you have chest pain, fainting, severe shortness of breath, or stroke symptoms, seek emergency care.

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Effective Orifice Area (Gorlin-style) Formula

The following formula is used to calculate the effective orifice area for a given set of cardiovascular parameters. 

EOA (cm²) = CO (mL/min) ÷ [HR (beats/min) × SEP (s) × 44.3 × √(mean gradient (mmHg))]

Variables:

  • EOA is the effective orifice area in cm²
  • CO is the cardiac output in milliliters per minute (mL/min) (1 L/min = 1000 mL/min)
  • HR is the heart rate in beats per minute (beats/min)
  • SEP is the systolic ejection period in seconds (sec)
  • MG is the mean transvalvular pressure gradient in millimeters of mercury (mmHg)

References / further reading

For authoritative guidance on valve-area calculation assumptions and stenosis grading thresholds, consult major cardiology and echocardiography guidelines (e.g., ACC/AHA valve disease guidelines, ESC/EACTS guidelines, and ASE/EACVI echo recommendations) and standard hemodynamics references that describe the Gorlin equation and the continuity equation.

To calculate the effective orifice area, divide the cardiac output (in mL/min) by 44.3 times the product of the heart rate, systolic ejection period, and the square root of the mean gradient (in mmHg).

What is an Effective Orifice Area?

The effective orifice area (EOA) is a measure used in cardiology to quantify the size of the opening through which blood flows in the heart, particularly through heart valves. It is an important parameter for assessing the severity of valve stenosis, which is a condition where the valve opening is narrowed, restricting blood flow. In practice, valve area/EOA can be estimated using different methods such as the Gorlin equation (cardiac catheterization/hemodynamics) or the continuity equation (echocardiography). A smaller EOA indicates a more severe stenosis, which can lead to increased cardiac workload and reduced efficiency of blood circulation.

How to Calculate Effective Orifice Area?

The following steps outline how to calculate the Effective Orifice Area.

  1. First, determine the cardiac output (CO) (often reported in L/min; convert to mL/min by multiplying by 1000 if needed).
  2. Next, determine the heart rate (HR) in beats per minute.
  3. Next, determine the systolic ejection period (SEP) in seconds.
  4. Next, determine the mean gradient (MG) in millimeters of mercury (mmHg).
  5. Finally, calculate the Effective Orifice Area using the formula EOA = CO(mL/min) / [44.3 × HR × SEP × √MG].
  6. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Cardiac Output (CO) = 5 L/min (5000 mL/min)

Heart Rate (HR) = 70 beats/min

Systolic Ejection Period (SEP) = 0.3 sec

Mean Gradient (MG) = 10 mmHg