What causes the dicrotic notch on the Wiggers diagram?

The dicrotic notch, or incisura, is a small dip in the aortic pressure trace as the aortic valve snaps shut at the end of ejection. Closure is accompanied by a brief backflow of blood toward the ventricle; aortic pressure then rises slightly (the dicrotic wave) before declining slowly through diastole. On the diagram it lines up with S2 and the start of isovolumetric relaxation.

Where do S3 and S4 fall on the Wiggers diagram?

S3 falls in early diastole, during rapid ventricular filling just after the mitral valve opens. It can be normal in children, in adults up to about age 40 and in pregnancy, but otherwise suggests a dilated, dysfunctional ventricle. S4 falls in late diastole, during atrial contraction after the P wave and just before S1. It reflects the atrial kick into a stiff ventricle, is always abnormal and is absent in atrial fibrillation.

What do the a, c and v waves represent?

They are the three peaks of atrial pressure. The a wave is atrial contraction after the P wave. The c wave appears in early systole as the closed AV valve bulges back into the atrium during isovolumetric contraction. The v wave is atrial filling against the closed AV valve during ventricular systole; it peaks just before the AV valve opens and is followed by the y descent.

How does the Wiggers diagram relate to the pressure-volume loop?

A pressure-volume loop plots LV pressure against LV volume from the same cardiac cycle. Its four corners are the four valve events: mitral closure at end-diastolic volume, aortic opening, aortic closure at end-systolic volume and mitral opening. The two vertical sides are the isovolumetric phases, the width of the loop is the stroke volume and the area inside it is the stroke work.

Do heart valves make a sound when they open?

Healthy valves open silently; the normal heart sounds come from closures, S1 from the AV valves and S2 from the semilunar valves. A sound at an opening means an abnormal valve or vessel: an ejection click just after S1 in congenital aortic or pulmonic stenosis or severe pulmonary hypertension, and an opening snap just after S2 in mitral stenosis, where a snap closer to S2 means more severe stenosis.

Wiggers Diagram: Cardiac Cycle Phases & Heart Sounds

A Wiggers diagram lines up aortic, left ventricular (LV) and left atrial (LA) pressure, LV volume, the ECG and the heart sounds on one time axis, and every valve event is a pressure crossing. The mitral valve closes (S1) when LV pressure rises above LA pressure, the aortic valve opens when LV pressure exceeds aortic pressure, the aortic valve closes (S2 and the dicrotic notch) when LV pressure falls below aortic pressure, and the mitral valve opens when LV pressure drops below LA pressure. The two isovolumetric phases are the only times all the valves are closed, so LV volume stays flat while pressure shoots up (right after the QRS) or falls away (right after S2).

The four valve events: learn these first

Valve event	Pressure crossing	What marks it	Phase it starts
Mitral closes	$P_{LV} > P_{LA}$	S1, just after the QRS; LV volume is at its maximum (EDV)	Isovolumetric contraction
Aortic opens	$P_{LV} > P_{Ao}$ (at aortic diastolic pressure)	Silent normally; LV and aortic traces merge	Ejection
Aortic closes	$P_{Ao} > P_{LV}$	S2 (A2) and the dicrotic notch on the aortic trace; LV volume is at its minimum (ESV)	Isovolumetric relaxation
Mitral opens	$P_{LA} > P_{LV}$	Silent normally; LA v wave peaks, then the y descent	Rapid filling

Recite these four in order and you can redraw the diagram. Closures make the normal heart sounds; openings are silent unless the valve is abnormal. The same four events are the four corners of the LV pressure-volume loop, drilled in the pressure-volume loop Q-bank breakdown.

The seven phases in one table

#	Phase	ECG anchor	Valves	LV pressure	LV volume	Waves and sounds
1	Atrial contraction	Follows the P wave	Mitral open, aortic closed	Small rise	Final top-up to EDV (about 120 mL)	a wave; S4 if the ventricle is stiff
2	Isovolumetric contraction	Begins with the QRS	All closed	Steep rise (maximal dP/dt)	Flat	S1; c wave
3	Rapid ejection	—	Aortic open	Rises to its peak	Falls fast	Normally silent; LA pressure dips (x′ descent)
4	Reduced ejection	T wave, about 200 ms after the QRS	Aortic open	Falls slightly below aortic pressure; blood keeps moving by momentum	Falls slowly to ESV (about 50 mL)	LA pressure climbs
5	Isovolumetric relaxation	After the T wave	All closed	Steep fall	Flat	S2; dicrotic notch; the v wave peaks at the end
6	Rapid filling	—	Mitral open	Keeps falling briefly, then rises slowly	Rises fast	y descent; S3 in a dilated ventricle
7	Reduced filling (diastasis)	Ends at the next P wave	Mitral open	Slowly rising	Slow rise	Filling slows

Most filling is passive (phases 6 and 7). Textbook estimates of the atrial kick in a resting heart range from about 10% to 20–30% of ventricular filling, and it can supply up to about 40% at fast heart rates, when there is less time for passive filling.

Normal pressures to know

Site	Average pressure (mm Hg)
Right atrium	Mean 3
Right ventricle	25 systolic / 4 end-diastolic
Pulmonary artery	25 / 9 (mean 15)
Pulmonary artery wedge	Mean 9
Left atrium	Mean 8; a wave 10, v wave 13
Left ventricle	130 systolic / 9 end-diastolic
Brachial artery	130 / 70 (mean 85)

An open valve makes two chambers behave as one: during ejection LV and aortic pressures differ by only a few mm Hg, and the wedge pressure approximates mean LA pressure and LV end-diastolic pressure.

Atrial waves: a, c, v and the neck veins

The LA trace, and the jugular venous pulse that mirrors the right atrium, has three peaks and two descents:

a wave: atrial contraction, right after the P wave. It disappears in atrial fibrillation. Giant cannon a waves appear in AV dissociation, when the atrium contracts against a closed tricuspid valve (see the AV block cheat sheet). Large a waves also occur with a stiff right ventricle (pulmonary hypertension, pulmonic stenosis) or tricuspid stenosis.
x descent: atrial relaxation, extended as the valve ring is pulled down during ejection.
c wave: early systole, as the closed AV valve bulges back into the atrium during isovolumetric contraction (in the neck, the carotid pulse contributes).
v wave: the atrium fills against a closed AV valve during systole; it peaks just before the valve opens. Very prominent v waves in the neck point to tricuspid regurgitation.
y descent: the AV valve opens and the atrium empties. It is abrupt when a rigid ventricle or pericardium stops filling suddenly (restrictive cardiomyopathy, constrictive pericarditis). A steep x descent is typical of cardiac tamponade.

Heart sounds and clicks on the timeline

Sound	Where it falls	Cause	Board associations
S1	Start of systole, just after the QRS	Mitral, then tricuspid, closure	Loud in mitral stenosis; soft in first-degree AV block
S2	End of systole, after the T wave	Aortic (A2), then pulmonic (P2), closure	Splits on inspiration; wide fixed split in ASD; paradoxical split in LBBB or aortic stenosis
S3	Early diastole, rapid filling	Filling of a dilated, noncompliant ventricle	Can be normal in children, up to about age 40 and in pregnancy; otherwise ventricular dysfunction
S4	Late diastole, just before S1	Atrial kick into a stiff ventricle	LVH, active ischemia or recent MI; always abnormal; absent in atrial fibrillation
Ejection click	Early systole, very near S1	Congenital aortic or pulmonic stenosis; severe pulmonary hypertension	Does not move with maneuvers, unlike the prolapse click
Mid-systolic click	Mid to late systole	Mitral valve prolapse	Moves toward S1 with standing or Valsalva
Opening snap	Early diastole, just after S2	Stiff mitral leaflet snaps open as LV pressure falls below LA pressure	Mitral stenosis; the closer to S2, the more severe

Gallop rhythm hooks: "Ken-TUCK-y" = S1–S2–S3 and "TEN-nes-see" = S4–S1–S2.

Murmurs sit on the same timeline. Systolic murmurs fall between S1 and S2: aortic and pulmonic stenosis are mid-systolic crescendo–decrescendo, while mitral regurgitation, tricuspid regurgitation and VSD are holosystolic. Diastolic murmurs are always abnormal: early diastolic means aortic or pulmonic regurgitation, mid-diastolic means mitral or tricuspid stenosis. The full lesion list is in the heart murmurs USMLE table.

Volumes on the diagram

Stroke volume is EDV − ESV (about 120 − 50 = 70 mL), and ejection fraction is stroke volume ÷ EDV. More preload raises EDV and stroke volume (Frank-Starling), more afterload raises ESV and lowers stroke volume, and more contractility lowers ESV and raises stroke volume.

Exam traps

Flat volume means isovolumetric. Rising pressure: the mitral valve just closed (after the QRS). Falling pressure: the aortic valve just closed (after the T wave).
The dicrotic notch is on the aortic trace, not the LV trace. It marks aortic closure, S2 and the end of ejection.
Ejection outlasts the pressure crossover: in reduced ejection, LV pressure dips slightly below aortic pressure, yet blood keeps flowing on momentum.
No a wave and no S4 in atrial fibrillation; cannon a waves mean AV dissociation.
Tachycardia shortens diastole, so S3 and S4 can merge into a summation gallop and the atrial kick matters more.

Worked example (Q-bank style)

Vignette. A 67-year-old man with long-standing hypertension has exertional dyspnea. An S4 is heard at the apex, and the ECG shows left ventricular hypertrophy. A Wiggers diagram marks point X just after the QRS complex: LV pressure is rising steeply, LV volume is unchanged, and the LA trace shows a small upward bump. Which valve event marks the start of the phase that contains point X?

A. Aortic valve opens B. Mitral valve closes C. Mitral valve opens D. Aortic valve closes E. Rapid ventricular filling begins

Answer: B. Just after the QRS, with pressure rising and volume flat, point X lies in isovolumetric contraction. That phase begins when LV pressure exceeds LA pressure and the mitral valve closes, producing S1; the small LA bump is the c wave.

Choice	Why it tempts	Why it is wrong
A. Aortic valve opens	Early systole, pressure rising	It ends isovolumetric contraction; LV volume would start to fall
C. Mitral valve opens	Atrial waves suggest mitral activity	It happens in early diastole, when LV pressure is low and volume starts to rise
D. Aortic valve closes	Closures make sounds and notches	That is S2 and the dicrotic notch, after the T wave, with pressure falling
E. Rapid filling begins	"Something is changing"	Filling needs an open mitral valve and a rising volume, and it is where an S3 would occur

Follow-up: where is his S4? In late diastole, during atrial contraction after the P wave, just before S1 and point X: the atrial kick striking his stiff, hypertrophied ventricle. It would vanish if he developed atrial fibrillation.

The 10-second method for any Wiggers question:

Find the QRS (systole begins) and the T wave (ejection is ending).
Is LV volume flat (isovolumetric), falling (ejection) or rising (filling)?
Flat volume + rising pressure = mitral just closed; flat volume + falling pressure = aortic just closed.
S1 starts systole; S2 starts diastole.

Key takeaways

Four valve events, four pressure crossings: mitral closes (S1), aortic opens, aortic closes (S2, dicrotic notch), mitral opens.
Numbers: EDV about 120 mL, ESV about 50 mL, stroke volume about 70 mL; LV about 130/9 mm Hg; mean LA about 8 mm Hg.
Atrial waves: a = atrial contraction (gone in AF, cannon in AV dissociation), c = AV valve bulge, v = filling against a closed valve (big in tricuspid regurgitation).
Sounds: S3 = early filling of a dilated ventricle; S4 = atrial kick into a stiff ventricle; clicks and snaps mean abnormal valves.