The Wiggers diagram is one of those “everything clicks at once” graphics in cardiac physiology: it lines up electrical activity, pressures, valves, volume, and heart sounds on a single timeline—aka exactly the kind of integration USMLE loves.
The Wiggers diagram in one sentence (the whole point)
ECG triggers mechanical events → valves respond to pressure gradients → ventricular volume changes → heart sounds mark valve closure.
Your visual anchor: “Up–Down–Up–Down” (pressures) + “Open–Closed–Open–Closed” (valves)
Picture the left heart (LV + aorta + LA) as a 4-beat loop:
- Mitral OPEN → LV filling (volume up)
- Mitral CLOSE → isovolumetric contraction (pressure up, volume flat)
- Aortic OPEN → ejection (volume down)
- Aortic CLOSE → isovolumetric relaxation (pressure down, volume flat)
Mnemonic:
“Fill → Squeeze → Shoot → Relax”
- Fill = diastole (mitral open)
- Squeeze = iso-contraction (both closed)
- Shoot = ejection (aortic open)
- Relax = iso-relaxation (both closed)
The 5 core traces (what you must be able to narrate)
1) ECG
- P wave = atrial depolarization → atrial contraction follows shortly
- QRS = ventricular depolarization → starts systole
- T wave = ventricular repolarization → precedes relaxation
2) Left ventricular pressure
- Low during filling → sharp rise during iso-contraction → high during ejection → falls during iso-relaxation
3) Aortic pressure
- Rises during ejection (tracks LV while aortic valve open)
- Shows dicrotic notch when aortic valve closes
4) Left atrial pressure (high-yield a, c, v waves)
- a wave: atrial contraction (after P wave)
- c wave: bulging of closed mitral valve during LV contraction
- v wave: venous filling of atrium against closed mitral valve (peaks just before mitral opens)
5) LV volume
- Increases during diastolic filling
- Plateaus during isovolumetric contraction (both valves closed)
- Decreases during ejection
- Plateaus during isovolumetric relaxation (both valves closed)
Phases you should be able to label (Step-style)
| Phase | Valves | LV Pressure | LV Volume | Key events |
|---|---|---|---|---|
| Atrial systole | Mitral open, Aortic closed | slight ↑ | slight ↑ (“atrial kick”) | a wave; contributes to S4 if stiff ventricle |
| Isovolumetric contraction | Both closed | big ↑ | no change | S1 (mitral closes); c wave |
| Rapid ejection | Aortic open | high | ↓↓↓ | Aortic pressure rises |
| Reduced ejection | Aortic open | starts ↓ | ↓ | T wave occurs near here |
| Isovolumetric relaxation | Both closed | big ↓ | no change | S2 (aortic closes); dicrotic notch |
| Rapid filling | Mitral open | low | ↑↑ | S3 may be heard (normal in kids/pregnancy; HF in older) |
| Reduced filling (diastasis) | Mitral open | low | slow ↑ | longest at slow HR; disappears at high HR |
Heart sounds: fastest way to orient yourself
- S1 = AV valves close (mitral/tricuspid) → start systole
- Loud S1: MS? (often loud early), short PR, hyperdynamic
- S2 = semilunar valves close (aortic/pulmonic) → end systole
- Physiologic splitting increases with inspiration (P2 delayed)
- S3 = rapid passive filling (early diastole)
- Think dilated ventricle / volume overload (CHF, MR) in adults
- S4 = atrial kick into stiff ventricle (late diastole)
- Think LVH, restrictive cardiomyopathy; absent in atrial fibrillation
The two “isovolumetric” phases (USMLE favorite)
Both valves closed → volume constant → pressure changes fast.
- Isovolumetric contraction: starts right after QRS, ends when LV pressure > aortic pressure (aortic opens)
- Isovolumetric relaxation: starts after T wave region, ends when LV pressure < LA pressure (mitral opens)
Dicrotic notch (don’t miss this)
Dicrotic notch = aortic valve closure causing a brief rise in aortic pressure from elastic recoil and retrograde flow.
If you see the notch, you’re at S2 / end systole.
One-liner “pressure-gradient rule” (works every time)
- Mitral opens when
- Aortic opens when
- Valves close when the inequality flips (and closure = heart sound)
High-yield Step correlations (quick hits)
How preload/afterload/contractility reshape the loop (and the Wiggers story)
| Change | What happens to SV? | What happens to ESV/EDV? | Why it matters |
|---|---|---|---|
| ↑ Preload | ↑ SV | ↑ EDV | Frank-Starling (more filling → more ejection) |
| ↑ Afterload | ↓ SV | ↑ ESV | Harder to eject → more blood left behind |
| ↑ Contractility | ↑ SV | ↓ ESV | Stronger squeeze → empties more |
Murmurs mapped onto the Wiggers timeline
- Systolic murmur = between S1 and S2
- AS (crescendo–decrescendo), MR (holosystolic)
- Diastolic murmur = after S2
- AR (early diastolic decrescendo), MS (opening snap + rumble)
Pro tip: murmurs are “valve flow problems,” while S1/S2 are valve closure sounds.
Micro-cheat: the “4 valve events” you must recite
- Mitral closes → S1 → iso-contraction begins
- Aortic opens → ejection begins
- Aortic closes → S2 + dicrotic notch → iso-relaxation begins
- Mitral opens → rapid filling (possible S3)
If you can say those four in order, you can rebuild the entire diagram under pressure.
Final one-page mental picture (say it out loud)
P → atria squeeze (a wave, tiny volume bump) → QRS → mitral shuts (S1) → LV pressure rockets (iso-contraction) → LV beats aorta → aortic opens (eject; volume falls) → T → aortic shuts (S2, notch) → LV relaxes fast (iso-relaxation) → LV drops below LA → mitral opens (rapid fill, maybe S3) → repeat.