Venous return and the Guyton curves !
- Mechanism
- Exam priority: medium
The heart can only pump the blood that reaches it. Venous return depends on the gap between venous pressure and right atrial pressure.
Updated 2026-11-01
Also called: Mean systemic filling pressure
See it in 3D: Superior vena cava · Inferior vena cava · Right atrium
What it is
In a steady state, what the heart pumps equals what comes back through the veins. Venous return is driven by the mean systemic filling pressure, set by blood volume and venous tone, against right atrial pressure. Crossing the venous return curve with the cardiac function curve gives the patient's actual cardiac output and atrial pressure.
How it works, step by step
- The volume that stretches vessels beyond their unstressed volume creates the mean systemic filling pressure.
- Blood flows from the peripheral veins to the right atrium down that pressure difference.
- If the heart pumps more, RA pressure falls and the gradient rises: more blood comes in.
- The heart answers more filling with a larger stroke volume (Frank–Starling): the two curves settle at one point.
- Hemorrhage lowers the mean filling pressure: the venous curve shifts left and output falls.
- Sympathetic venoconstriction and renal fluid retention raise the mean filling pressure and restore output.
Equations
- Pmsf
- mean systemic filling pressure
- PRA
- right atrial pressure
- RVR
- resistance to venous return
In a steady state venous return equals cardiac output.
Reference values (resting adult)
| Parameter | Value |
|---|---|
| Mean systemic filling pressure | ≈7 mmHg |
| Right atrial pressure | ≈0–5 mmHg |
| Cardiac output = venous return | ≈5 L/min |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Regulation
- +Larger blood volume: Mean filling pressure rises: more return at the same atrial pressure.
- +Sympathetic venoconstriction: Cuts venous capacitance and moves blood toward the heart.
- +Muscle pump and breathing (negative intrathoracic pressure): Push blood from the legs and abdomen into the chest.
- −High intrathoracic pressure (positive-pressure ventilation, tension pneumothorax): Raises RA pressure and shrinks the return gradient.
- −Hemorrhage or venodilation: Mean filling pressure falls and output drops.
Clinical notes
- In heart failure the cardiac curve falls; the kidneys retain salt and water, mean filling pressure rises and output recovers at the price of high venous pressures (edema, congestion).
- In hypovolemic shock the fall in mean filling pressure explains why replacing volume restores output.
- Positive-pressure ventilation can drop output in a hypovolemic patient because it lowers venous return.
Test yourself
Think of the answer, then tap the question to see it.
What happens to venous return if right atrial pressure rises to equal the mean systemic filling pressure?
It becomes zero: there is no longer a pressure gradient moving blood from the veins to the heart.
Why does lowering RA pressure below zero stop increasing venous return?
The great veins entering the chest collapse at negative pressures and limit flow: the curve plateaus.
How does the venous return curve shift after a rapid transfusion?
It shifts in parallel to the right: mean filling pressure rises and return increases at any atrial pressure.
In chronic heart failure, how does renal fluid retention help and how does it harm?
It raises the mean filling pressure and restores output, but it also raises venous and atrial pressures, causing congestion and edema.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Cardiac output and what sets it
- The Frank–Starling mechanism
- Vascular compliance and capacitance
- Central venous pressure and the jugular pulse
- Shock physiology
- Heart failure physiology
Related conditions
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 20.2 Blood Flow, Blood Pressure, and Resistance (OpenStax (Rice University), 2022); 19.4 Cardiac Physiology (OpenStax (Rice University), 2022); Heart Failure (Congestive Heart Failure) (StatPearls (NCBI Bookshelf), 2025); Hypovolemia and Hypovolemic Shock (StatPearls (NCBI Bookshelf), 2025); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 20). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.