A 73-year-old man presents to your clinic for a routine checkup. His medical history is notable for a previous myocardial infarction. He states that he has not seen a doctor in "many years". He has no complaints. When you auscultate over the cardiac apex with the bell of your stethoscope, you notice an additional sound immediately preceding S1. This extra heart sound is most likely indicative of which of the following processes?

Decreased left ventricular compliance

Increased left ventricular compliance

Decreased left ventricular filling volume

Increased left ventricular filling volume

A 64-year-old man presents to the emergency department because he has been experiencing increased shortness of breath for the last 2 weeks. Specifically, he says that he can barely walk up the stairs to his apartment before he feels winded. In addition, he has been waking up at night gasping for breath and has only been able to sleep propped up on 2 more pillows than usual. Physical exam reveals jugular venous distention as well as pitting lower extremity edema. Which of the following abnormal sounds will most likely be heard in this patient?

Extra heart sound in early diastole

Extra heart sound in late diastole

Parasternal holosystolic murmur

A 31-year-old woman presents to the clinic with shortness of breath, palpitations, and fatigue. She has had these symptoms over the last several weeks. She had been tolerating these symptoms until last night when she could not fall asleep due to palpitations. She has a past medical history of infective endocarditis 6 months ago that was successfully treated with antibiotics. She does not smoke or drink alcohol. Her blood pressure is 138/89 mm Hg and her pulse is 76/min and regular. The cardiac exam reveals a soft S1, S3 gallop, a hyperdynamic apex beat, and a pansystolic murmur that radiates to the axilla on auscultation. Echocardiography reveals incompetence of one of the valves. Which of the following sites is the best position to auscultate this defect?

5th intercostal space at the midclavicular line on the left side

Medial end of the 2nd intercostal space on the right side

4th intercostal space at the midclavicular line on the left side

Medial end of the 2nd intercostal space on the left side

Right lower end of the body of the sternum

A 52-year-old man comes to the physician for a routine health maintenance examination. He has not seen a physician for 10 years. He works as a telemarketer and does not exercise. Cardiac examination shows a dull, low-pitched sound during late diastole that is best heard at the apex. The sound is loudest in the left lateral decubitus position and during end-expiration. Which of the following is the most likely cause of this finding?

Concentric left ventricular hypertrophy

Fusion of mitral valve leaflets

A 27-year-old male arrives in the emergency department with a stab wound over the precordial chest wall. The patient is in distress and is cold, sweaty, and pale. Initial physical examination is significant for muffled heart sounds, distended neck veins, and a 3 cm stab wound near the left sternal border. Breath sounds are present bilaterally without evidence of tracheal deviation. Which of the following additional findings would be expected on further evaluation?

15 mmHg decrease in systolic blood pressure with inspiration

Decrease in central venous pressure by 5 mmHg with inspiration

Decrease in the patient's heart rate by 15 beats per minute with inspiration

Steadily decreasing heart rate to 60 beats per minute

Elevated blood pressure to 170/110

A 45-year-old man is brought to the emergency department after a car accident with pain in the middle of his chest and some shortness of breath. He has sustained injuries to his right arm and leg. He did not lose consciousness. His temperature is 37°C (98.6°F), pulse is 110/min, respirations are 18/min, and blood pressure is 90/60 mm Hg. He is alert and oriented to person, place, and time. Examination shows several injuries to the upper extremities and chest. There are jugular venous pulsations 10 cm above the sternal angle. Heart sounds are faint on cardiac examination. The lungs are clear to auscultation. An ECG is shown. Which of the following is the most appropriate next step in management?

Contrast-enhanced CT angiography

Contrast esophagram with gastrografin

A 65-year-old woman comes to the physician because of a 3-month history of intermittent palpitations and shortness of breath. Cardiopulmonary examination shows no other abnormalities. An ECG shows an absence of P waves, an oscillating baseline, and irregular RR intervals at a rate of approximately 95 beats per minute. The difference between atrial and ventricular rates in this patient is most likely due to which of the following?

Temporary inactivation of Na+ channels in the AV node

Prolonged influx through voltage-gated Ca2+ channels in the bundle of His

Transient activation of K+ current in Purkinje fibers

Inhibition of the Na+/K+-ATPase pump in ventricular cells

Limited speed of conduction through the left bundle branch

A 72-year-old man with severe aortic regurgitation and compensated heart failure is being evaluated for surgical intervention. His echocardiogram shows LV end-diastolic dimension of 7.5 cm, ejection fraction of 45%, and severe aortic regurgitation with a regurgitant fraction of 60%. Pressure-volume loop analysis shows a markedly widened loop with increased stroke work. Evaluate the compensatory mechanisms maintaining his cardiac output and predict the timing for surgical intervention based on cardiac cycle mechanics.

Surgery is indicated now because the increased stroke work indicates the ventricle is operating at near-maximal preload reserve with impending decompensation despite preserved ejection fraction

Surgery should be delayed until ejection fraction falls below 35% because current compensatory mechanisms are adequate as evidenced by maintained cardiac output

Surgery is contraindicated due to excessive left ventricular dimensions indicating irreversible remodeling with poor surgical outcomes

Medical management with vasodilators should continue indefinitely because reduced afterload optimizes the pressure-volume relationship

Surgery should wait until symptoms develop because pressure-volume loop changes alone do not predict outcomes in valvular disease

Heart sounds and their origin for USMLE Step 3: High-Yield Physiology Lessons

S1 Heart Sound - Lub Dub Start

Origin: Closure of atrioventricular (mitral & tricuspid) valves.
- Marks the beginning of isovolumetric ventricular systole.
- Components: Mitral (M1) closes just before Tricuspid (T1).
Auscultation:
- Loudest at the heart apex (mitral area).
- Coincides with the carotid pulse upstroke.

Wiggers Diagram: Cardiac Cycle, ECG, and Heart Sounds

Intensity Variations:
- ↑ Loud S1: Short PR interval, mitral stenosis, high output states.
- ↓ Soft S1: Long PR interval, mitral regurgitation, poor LV function.

⭐ The intensity of S1 is primarily determined by the mitral valve's position at the start of systole; a wide-open valve (short PR) slams shut loudly.

S2 Heart Sound - The Dub & Split

Origin: Closure of semilunar (Aortic & Pulmonic) valves at the end of systole.
Components: Aortic valve (A2) closure followed by Pulmonic valve (P2) closure. A2 is normally louder.

Physiological Splitting

During Inspiration:
- ↓ Intrathoracic pressure → ↑ venous return to the right heart.
- ↑ RV filling → prolonged RV ejection → delayed P2 closure.
- Result: Audible split (A2, then P2).
During Expiration:
- ↑ Intrathoracic pressure → ↓ venous return.
- RV ejection is shorter → A2 and P2 are fused or nearly synchronous.

Physiological Splitting of S2

⭐ Fixed Splitting: A wide S2 split that does not vary with respiration is a classic sign of an Atrial Septal Defect (ASD). The left-to-right shunt increases RA and RV volumes, delaying P2 closure regardless of the respiratory cycle.

S3 & S4 Sounds - Pathologic Gallops

S3 (Ventricular Gallop): "Slosh-ing IN"
- Timing: Early diastole, after S2. Low-pitched sound.
- Mechanism: Rapid ventricular filling into a dilated, high-volume ventricle.
- Associations (Pathologic):
  - Systolic heart failure (dilated cardiomyopathy)
  - Mitral or tricuspid regurgitation
- Physiologic: Can be normal in children, athletes, and pregnancy.
- 📌 Cadence: Ken-TUCK-y (S1-S2-S3)
S4 (Atrial Gallop): "a STIFF wall"
- Timing: Late diastole, before S1. Low-pitched sound.
- Mechanism: Atrial kick against a stiff, noncompliant ventricle.
- Associations (Always Pathologic):
  - Ventricular hypertrophy (long-standing HTN, aortic stenosis)
  - Hypertrophic cardiomyopathy
- 📌 Cadence: TEN-nes-see (S4-S1-S2)

Phonocardiogram of S1, S2, S3, and S4 heart sounds

⭐ S4 is characteristically absent in atrial fibrillation because the required coordinated "atrial kick" is lost.

Auscultation Points - Finding the Sounds

Auscultation points are specific locations where valve sounds radiate and are best heard, distinct from their anatomical sites. Use the diaphragm for high-pitched sounds (S1, S2) and the bell for low-pitched sounds (S3, S4).

📌 Mnemonic: All Physicians Earn Their Money.

Cardiac Auscultation Points (APETM)

Aortic: 2nd right intercostal space (ICS).
Pulmonic: 2nd left ICS.
Tricuspid: 4th left ICS.
Mitral: 5th left ICS, midclavicular line (apex).

⭐ Erb's point (3rd left ICS) is ideal for hearing S2 splits and certain murmurs like aortic regurgitation.

High‑Yield Points - ⚡ Biggest Takeaways

S1 ("lub") marks the start of systole and is caused by the closure of the mitral and tricuspid valves.

S2 ("dub") marks the end of systole and is caused by the closure of the aortic and pulmonic valves.

Physiological splitting of S2 occurs during inspiration due to delayed pulmonic valve closure.

An S3 sound indicates volume overload and is common in heart failure.

An S4 sound suggests a stiff, noncompliant ventricle, often due to chronic hypertension.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play