[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Cardiovascular](https://durgical.com/en/physiology/#s-cardio) › The Frank–Starling mechanism [Physiology](https://durgical.com/en/physiology/) · [Cardiovascular](https://durgical.com/en/physiology/#s-cardio) # The Frank–Starling mechanism - Mechanism - Exam priority: high The more the heart is filled, the harder it squeezes, so it pumps out whatever blood comes back to it. Updated 2026-11-01 Also called: Starling's law of the heart, Heterometric autoregulation **See it in 3D:** [Left ventricle](https://durgical.com/en/anatomy/left-ventricle/) · [Right ventricle](https://durgical.com/en/anatomy/right-ventricle/) ## Key points - ↑ End-diastolic volume (preload) → ↑ stroke volume, with no change in contractility. - Cellular basis: stretch brings sarcomeres toward optimal overlap (≈ 2.2 µm) and raises myofilament sensitivity to Ca²⁺. - It balances the two ventricles: if the RV pumps more for a few beats, more blood reaches the LV and it pumps more too. - A change in contractility (inotropy) moves to a different curve; a change in preload moves along the same curve. - In a failing heart the curve is flat: more filling raises pressure (congestion) with little gain in output. ## What it is Within physiological limits, a ventricle that is stretched more in diastole contracts more strongly in the next systole. This intrinsic property matches the output of the heart to venous return beat by beat, and keeps the outputs of the right and left ventricles equal over time. ## Key facts - Starling curve: x axis = preload (EDV, or atrial / wedge pressure), y axis = stroke volume or cardiac output. - Sympathetic stimulation and inotropes shift the curve up and left; heart failure, negative inotropes and acidosis shift it down. - In the clinic, a fluid challenge tests where a patient is on the curve: responders are on the steep part. ## How it works, step by step - More venous return fills the ventricle more in diastole (higher EDV). - Myocytes stretch toward the length where actin and myosin overlap best. - Stretch increases the Ca²⁺ sensitivity of troponin and narrows the gap between filaments. - More cross-bridges form at the same Ca²⁺ level, so force rises. - The ventricle ejects more (higher stroke volume) and ends near its usual end-systolic volume. - Beyond the plateau, extra filling only raises diastolic pressure: congestion and edema without more output. ### Left-ventricular pressure–volume loop **EDV** 150 mL **ESV** 62 mL **SV** 88 mL **EF** 59% **ESP** 132 mmHg #### ↑ Preload ↑ Preload (more end-diastolic volume, e.g. fluids): the loop stretches to the right and SV rises by Frank–Starling with the same contractility. ESV changes little. Tap a corner of the loop (MC, AO, AC, MO) to see the valve event. - Current loop - Normal loop - ESPVR (contractility, Ees) - EDPVR (passive filling) - Ea (arterial afterload) - Stroke volume (SV) Raise preload and see stroke volume grow while the end-systolic point stays on the same line. ## Clinical notes - Hypovolemia puts the heart on the low, steep part of the curve: fluid raises output. - In decompensated heart failure diuretics move the patient left along a flat curve: less congestion with little loss of output. ## Memory aid A rubber band shot farther the more you pull it back, until it is overstretched. ## Test yourself Think of the answer, then tap the question to see it. ## What is the cellular basis of the Frank–Starling mechanism? Stretch brings sarcomeres closer to optimal length and increases myofilament Ca²⁺ sensitivity, so more cross-bridges form at the same Ca²⁺ level. ## How does the Frank–Starling mechanism keep left and right ventricular outputs equal? If one ventricle pumps more, the other receives more venous return a few beats later, stretches more and raises its output to match. ## On a Starling curve, how do you tell a change in preload from a change in contractility? Preload moves the point along the same curve; contractility shifts the whole curve up (more) or down (less). ## Why does giving more fluid to a patient with severe heart failure often worsen breathlessness without raising output? The patient is on the flat part of a depressed curve: more volume raises filling pressures and pulmonary congestion but adds little stroke volume. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/the-frank-starling-mechanism/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Left ventricle](https://durgical.com/en/anatomy/left-ventricle/) - [Right ventricle](https://durgical.com/en/anatomy/right-ventricle/) ## Related topics - [Preload, afterload and contractility](https://durgical.com/en/physiology/preload-afterload-and-contractility/) - [Cardiac output and what sets it](https://durgical.com/en/physiology/cardiac-output-and-what-sets-it/) - [The ventricular pressure–volume loop](https://durgical.com/en/physiology/the-ventricular-pressure-volume-loop/) - [Venous return and the Guyton curves](https://durgical.com/en/physiology/venous-return-and-the-guyton-curves/) - [Heart failure physiology](https://durgical.com/en/physiology/heart-failure-physiology/) ## Related conditions - [Heart failure](https://durgical.com/en/conditions/heart-failure/) - [Hypovolaemic shock](https://durgical.com/en/conditions/hypovolaemic-shock/) [← All of physiology](https://durgical.com/en/physiology/) 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: [19.4 Cardiac Physiology](https://openstax.org/books/anatomy-and-physiology-2e/pages/19-4-cardiac-physiology) (OpenStax (Rice University), 2022); [Heart Failure (Congestive Heart Failure)](https://www.ncbi.nlm.nih.gov/books/NBK430873/) (StatPearls (NCBI Bookshelf), 2025); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 9). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/physiology/the-frank-starling-mechanism/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/the-frank-starling-mechanism/