1. “Preload” suggests the heart needs to be stretched to pump more. Like it’s a spring. That idea comes from Starling’s Law – but the clinical interpretation is flawed.

2. Starling’s Law doesn’t mean stretch causes increased cardiac output. It means: if more blood arrives, more gets pumped out – up to a point. It’s a passive relationship – a servo control mechanism, as we said in the last thread – not an active driver.

3. So what actually increases cardiac output? Not stretch. Not “loading the myocardium.” 👉 It’s venous return – driven by a pressure gradient.

4. That gradient starts upstream: From the small veins and venules To the right atrium. And it depends on mean systemic pressure (Pms) – not “preload.”

5. Add fluid? You’re not “preloading the heart.” You’re raising Pms, increasing the pressure head for venous return.

6. The heart doesn’t control flow – it accepts it. In most cases, output rises because the system delivers more – not because the ventricle is stretched.

7. “Preload responsiveness” is a misnomer. You’re seeing Pms responsiveness, or venous return responsiveness – not stretch-induced contractility.

8. And remember: Arterial pressure has no effect on venous return. The driver is venular. Pms is close to venular pressure because most of the blood volume is in the venous system.

So let’s stop saying “preload.” It hides the real physiology. It misleads our language, our thinking, and often our prescribing.

What should we say instead? That’s up for debate — and each option has pros and cons. 🗳️ Poll in the next tweet. Vote + reply 👇

What term should we use instead of “preload”?

🧠 Here's some pros and cons for you to think about when answering👇

🗣️ Interested to hear other suggestions in the replies.

Start here 👇 Why “preload” is one of the most misleading terms in clinical physiology — and what we should say instead. https://x.com/icmteaching/stat...

@icmteaching I guess 'mean systemic pressure' tends to imply pressure as it applies to the entire system, not just the venous system. I voted for 'venular pressure' as the other 2 don't seem descriptive enough. (I'm not a Dr so my vote counts for nix really...😂)

@Kevin34050619 I like your thinking. Pms is the entire system but because most blood is in the venules the 2 pressures are very similar. That doesn’t help though does it 😂. I vacillate between them!

@icmteaching Excellent, thanks 👍🏼