USMLE Step 1 Cardiology: 8 High-Yield Practice Questions
Cardiology is one of the highest-yield Step 1 subjects — accounting for roughly 15–20% of tested content. Heart failure, congenital disease, arrhythmias, and valvular pathology all appear repeatedly. Work through these 8 questions before checking explanations.
A 4-year-old girl has a fixed, split S2 that does not vary with respiration. She has a systolic ejection murmur at the upper left sternal border. Echo shows right ventricular enlargement. What is the most likely diagnosis?
Explanation: ASD classically produces fixed splitting of S2 (the split does not vary with respiration) because the left-to-right shunt maintains constant right heart filling regardless of respiratory phase. The systolic ejection murmur results from increased flow across the pulmonary valve. RV enlargement follows chronic volume overload.
Q2Valvular Disease
A 65-year-old man with known aortic stenosis undergoes Valsalva maneuver during cardiac exam. The murmur of aortic stenosis would be expected to:
Explanation: Valsalva maneuver decreases venous return → decreases preload → decreases cardiac output and transvalvular gradient. Most murmurs decrease with Valsalva. The notable exceptions that INCREASE with Valsalva: hypertrophic obstructive cardiomyopathy (HOCM) and mitral valve prolapse (earlier click, longer murmur).
Q3Cyanotic Congenital Heart Disease
A neonate born at term turns blue when crying but is pink at rest. A PaO2 of 35 mmHg is unresponsive to 100% O2. Chest X-ray shows an 'egg on a string' heart. Most likely diagnosis?
Explanation: Transposition of the great arteries (TGA): the aorta arises from the right ventricle and the pulmonary artery from the left — creating two parallel circuits. Classic findings: 'egg on a string' (narrow mediastinum on CXR), cyanosis unresponsive to O2 (no mixing), presents at birth when the PDA closes. Treat immediately with prostaglandin E1 to keep PDA open, then surgical correction (arterial switch operation).
Q4Heart Failure
A 72-year-old woman with dyspnea on exertion has an S3 gallop, JVD, and bilateral pitting edema. EF on echo is 35%. The mechanism of her dyspnea is best explained by:
Explanation: EF 35% = systolic dysfunction (HFrEF). Reduced contractility → reduced ejection → increased end-systolic volume → increased LVEDP → pulmonary venous congestion → dyspnea. S3 = volume overload. JVD and edema = right-sided failure from chronic left-sided pressure. Diastolic dysfunction (HFpEF) has preserved EF ≥50% with reduced compliance.
Q5Cardiac Pharmacology
A patient with a mechanical aortic valve is on warfarin. He needs dental extraction. His INR is 2.5. What is the most appropriate management?
Explanation: Mechanical aortic valves carry high thromboembolism risk. Bridging with UFH or LMWH while warfarin is held perioperatively is required for high-risk mechanical valves. The target INR for mechanical aortic valves is 2.0–3.0; bileaflet valves in the aortic position may not require bridging for minor procedures per recent guidelines — but for dental extraction in a high-risk scenario, bridging is standard.
Q6Pericardial Disease
A patient presents with pulsus paradoxus, muffled heart sounds, and hypotension. JVP is elevated. ECG shows low-voltage QRS with electrical alternans. What is the diagnosis?
Explanation: Beck's triad of cardiac tamponade: hypotension, muffled heart sounds, JVD. Pulsus paradoxus (>10 mmHg drop in SBP during inspiration) and electrical alternans on ECG (alternating QRS axis from heart swinging in fluid) are pathognomonic. Treat: pericardiocentesis. Constrictive pericarditis also has elevated JVP but has Kussmaul's sign (JVP rises on inspiration) and pericardial knock.
Q7Coronary Artery Disease
A 55-year-old man presents 6 hours after onset of crushing chest pain. Troponin I is 8.2 ng/mL. ECG shows ST elevations in II, III, aVF. Which coronary artery is most likely occluded?
Explanation: Inferior STEMI (ST elevation in II, III, aVF) = right coronary artery (RCA) occlusion in 70–80% of cases. The RCA supplies the inferior wall of the LV, posterior-descending artery, SA node (60%), and AV node (80%). Complications of inferior MI: AV block, sinus bradycardia, right ventricular infarction (look for ST elevation in V4R).
Q8Cardiac Pharmacology
Digoxin toxicity is most likely to be precipitated by:
Explanation: Hypokalemia potentiates digoxin toxicity. Digoxin inhibits the Na/K-ATPase pump. In hypokalemia, reduced extracellular K+ increases digoxin binding to the pump → increased toxicity. Treat digoxin toxicity: correct hypokalemia, digoxin-specific antibody fragments (Digibind) for severe toxicity, avoid calcium (can worsen arrhythmias).
What are the most common cardiology topics on USMLE Step 1?
The highest-yield cardiology topics for Step 1 are: heart sounds and gallops (S3 vs S4), congenital heart disease (cyanotic vs acyanotic, shunt directions), valvular lesions and murmur maneuvers (Valsalva, squatting, hand grip), cardiac tamponade vs constrictive pericarditis, MI time course and cardiac biomarkers (troponin, CK-MB timing), and antiarrhythmic drug mechanisms (Vaughan-Williams classification).
How do you remember which murmurs increase with Valsalva?
Only two murmurs INCREASE with Valsalva (decreased preload): HOCM (hypertrophic obstructive cardiomyopathy) and MVP (mitral valve prolapse). All other murmurs decrease with Valsalva. Mnemonic: 'HOCM and MVP are the exceptions — they both increase with decreased preload (Valsalva, standing) and decrease with increased preload (squatting, leg raise).'
What is the difference between HFrEF and HFpEF?
HFrEF (heart failure with reduced ejection fraction): EF <40%, systolic dysfunction, dilated LV. Treated with ACE inhibitors/ARBs, beta-blockers, aldosterone antagonists, SGLT2 inhibitors, hydralazine/nitrates (in Black patients). HFpEF (preserved EF ≥50%): diastolic dysfunction, stiff LV, usually hypertensive/obese elderly patients. Treatment is primarily symptom management — diuretics, blood pressure control; no mortality-reducing therapy proven.
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