USMLE Step 1 Exam 2026–2027
Comprehensive Study Guide with High-Yield
Review, Practice Questions, Detailed
Explanations & Success Prep
1. A 55-year-old man with a history of hypertension presents with sudden-
onset, severe "tearing" chest pain that radiates to his back. His blood pressure
is 180/100 mmHg in the right arm and 140/80 mmHg in the left arm. Which
of the following is the most likely diagnosis?
• A. Acute myocardial infarction
• B. Pulmonary embolism
• C. Aortic dissection
• D. Pericarditis
Correct Answer: C. Aortic dissection
Rationale: Aortic dissection classically presents with sudden, severe tearing
chest pain that radiates to the back, along with pulse or blood pressure
differentials between arms. The blood pressure difference (180/100 vs.
140/80) is a key finding. Acute MI (A) typically presents with pressure-like
chest pain without pulse differentials. Pulmonary embolism (B) presents with
sudden dyspnea and pleuritic chest pain. Pericarditis (D) presents with sharp
chest pain that improves with leaning forward.
2. A 68-year-old woman with heart failure is prescribed digoxin. Which
electrolyte abnormality would most significantly increase her risk of digoxin
toxicity?
• A. Hyperkalemia
• B. Hypokalemia
• C. Hypercalcemia
, • D. Hyponatremia
Correct Answer: B. Hypokalemia
Rationale: Hypokalemia increases the risk of digoxin toxicity by enhancing
the binding of digoxin to the Na⁺/K⁺-ATPase pump. Hyperkalemia (A) actually
decreases the risk of toxicity. Hypercalcemia (C) can also increase the risk of
digoxin toxicity but is less significant than hypokalemia. Hyponatremia (D)
does not directly affect digoxin toxicity.
3. A 72-year-old man with a history of myocardial infarction is taking
warfarin. His INR is 5.5. Which of the following is the most appropriate
immediate management?
• A. Administer vitamin K orally
• B. Administer fresh frozen plasma
• C. Hold warfarin and monitor INR
• D. Administer protamine sulfate
Correct Answer: C. Hold warfarin and monitor INR
Rationale: For an INR of 5.5 without bleeding, holding warfarin and
monitoring INR is appropriate. Vitamin K (A) is indicated for INR > 5.0 with
bleeding risk or > 8.0 without bleeding. Fresh frozen plasma (B) is used for
bleeding with elevated INR. Protamine sulfate (D) is used for heparin reversal,
not warfarin.
4. A 45-year-old man presents with a blood pressure of 150/95 mmHg. His
physical examination reveals a bruit over the right renal artery. Which of the
following is the most likely cause of his hypertension?
• A. Primary hyperaldosteronism
• B. Renal artery stenosis
• C. Pheochromocytoma
• D. Cushing syndrome
,Correct Answer: B. Renal artery stenosis
Rationale: A bruit over the renal artery suggests renal artery stenosis as the
cause of hypertension (renovascular hypertension). Primary
hyperaldosteronism (A) presents with hypertension and hypokalemia without
a bruit. Pheochromocytoma (C) presents with episodic hypertension,
tachycardia, and headache. Cushing syndrome (D) presents with central
obesity, striae, and hypertension.
5. A 60-year-old man with a history of smoking and hypertension presents
with chest pain that occurs with exertion and resolves with rest. Which of the
following is the most likely diagnosis?
• A. Unstable angina
• B. Stable angina
• C. Prinzmetal angina
• D. Myocardial infarction
Correct Answer: B. Stable angina
Rationale: Stable angina is characterized by chest pain that occurs
predictably with exertion and resolves with rest or nitroglycerin. Unstable
angina (A) occurs at rest or with minimal exertion. Prinzmetal angina (C) is
caused by coronary vasospasm and often occurs at rest. Myocardial infarction
(D) presents with prolonged chest pain not relieved by rest.
6. A 55-year-old woman presents with dyspnea, fatigue, and peripheral
edema. Echocardiography reveals a thick, stiff left ventricle with reduced
filling. Which of the following is the most likely diagnosis?
• A. Dilated cardiomyopathy
• B. Hypertrophic cardiomyopathy
• C. Restrictive cardiomyopathy
• D. Constrictive pericarditis
, Correct Answer: C. Restrictive cardiomyopathy
Rationale: Restrictive cardiomyopathy is characterized by a stiff, non-
compliant ventricular wall with impaired filling, often due to infiltrative
diseases (e.g., amyloidosis). Dilated cardiomyopathy (A) presents with a
dilated, thin-walled ventricle and systolic dysfunction. Hypertrophic
cardiomyopathy (B) presents with asymmetric septal hypertrophy.
Constrictive pericarditis (D) presents with pericardial thickening and
calcification.
7. A 62-year-old man with a history of hypertension and diabetes is
prescribed lisinopril. Which of the following is the most important laboratory
value to monitor?
• A. Serum potassium
• B. Serum sodium
• C. Serum calcium
• D. Serum magnesium
Correct Answer: A. Serum potassium
Rationale: ACE inhibitors like lisinopril can cause hyperkalemia by reducing
aldosterone secretion. Serum potassium should be monitored. Sodium (B),
calcium (C), and magnesium (D) are not typically affected.
8. A 35-year-old woman presents with a murmur heard best at the apex,
radiating to the axilla. Which of the following is the most likely diagnosis?
• A. Aortic stenosis
• B. Mitral regurgitation
• C. Mitral stenosis
• D. Aortic regurgitation
Correct Answer: B. Mitral regurgitation
Comprehensive Study Guide with High-Yield
Review, Practice Questions, Detailed
Explanations & Success Prep
1. A 55-year-old man with a history of hypertension presents with sudden-
onset, severe "tearing" chest pain that radiates to his back. His blood pressure
is 180/100 mmHg in the right arm and 140/80 mmHg in the left arm. Which
of the following is the most likely diagnosis?
• A. Acute myocardial infarction
• B. Pulmonary embolism
• C. Aortic dissection
• D. Pericarditis
Correct Answer: C. Aortic dissection
Rationale: Aortic dissection classically presents with sudden, severe tearing
chest pain that radiates to the back, along with pulse or blood pressure
differentials between arms. The blood pressure difference (180/100 vs.
140/80) is a key finding. Acute MI (A) typically presents with pressure-like
chest pain without pulse differentials. Pulmonary embolism (B) presents with
sudden dyspnea and pleuritic chest pain. Pericarditis (D) presents with sharp
chest pain that improves with leaning forward.
2. A 68-year-old woman with heart failure is prescribed digoxin. Which
electrolyte abnormality would most significantly increase her risk of digoxin
toxicity?
• A. Hyperkalemia
• B. Hypokalemia
• C. Hypercalcemia
, • D. Hyponatremia
Correct Answer: B. Hypokalemia
Rationale: Hypokalemia increases the risk of digoxin toxicity by enhancing
the binding of digoxin to the Na⁺/K⁺-ATPase pump. Hyperkalemia (A) actually
decreases the risk of toxicity. Hypercalcemia (C) can also increase the risk of
digoxin toxicity but is less significant than hypokalemia. Hyponatremia (D)
does not directly affect digoxin toxicity.
3. A 72-year-old man with a history of myocardial infarction is taking
warfarin. His INR is 5.5. Which of the following is the most appropriate
immediate management?
• A. Administer vitamin K orally
• B. Administer fresh frozen plasma
• C. Hold warfarin and monitor INR
• D. Administer protamine sulfate
Correct Answer: C. Hold warfarin and monitor INR
Rationale: For an INR of 5.5 without bleeding, holding warfarin and
monitoring INR is appropriate. Vitamin K (A) is indicated for INR > 5.0 with
bleeding risk or > 8.0 without bleeding. Fresh frozen plasma (B) is used for
bleeding with elevated INR. Protamine sulfate (D) is used for heparin reversal,
not warfarin.
4. A 45-year-old man presents with a blood pressure of 150/95 mmHg. His
physical examination reveals a bruit over the right renal artery. Which of the
following is the most likely cause of his hypertension?
• A. Primary hyperaldosteronism
• B. Renal artery stenosis
• C. Pheochromocytoma
• D. Cushing syndrome
,Correct Answer: B. Renal artery stenosis
Rationale: A bruit over the renal artery suggests renal artery stenosis as the
cause of hypertension (renovascular hypertension). Primary
hyperaldosteronism (A) presents with hypertension and hypokalemia without
a bruit. Pheochromocytoma (C) presents with episodic hypertension,
tachycardia, and headache. Cushing syndrome (D) presents with central
obesity, striae, and hypertension.
5. A 60-year-old man with a history of smoking and hypertension presents
with chest pain that occurs with exertion and resolves with rest. Which of the
following is the most likely diagnosis?
• A. Unstable angina
• B. Stable angina
• C. Prinzmetal angina
• D. Myocardial infarction
Correct Answer: B. Stable angina
Rationale: Stable angina is characterized by chest pain that occurs
predictably with exertion and resolves with rest or nitroglycerin. Unstable
angina (A) occurs at rest or with minimal exertion. Prinzmetal angina (C) is
caused by coronary vasospasm and often occurs at rest. Myocardial infarction
(D) presents with prolonged chest pain not relieved by rest.
6. A 55-year-old woman presents with dyspnea, fatigue, and peripheral
edema. Echocardiography reveals a thick, stiff left ventricle with reduced
filling. Which of the following is the most likely diagnosis?
• A. Dilated cardiomyopathy
• B. Hypertrophic cardiomyopathy
• C. Restrictive cardiomyopathy
• D. Constrictive pericarditis
, Correct Answer: C. Restrictive cardiomyopathy
Rationale: Restrictive cardiomyopathy is characterized by a stiff, non-
compliant ventricular wall with impaired filling, often due to infiltrative
diseases (e.g., amyloidosis). Dilated cardiomyopathy (A) presents with a
dilated, thin-walled ventricle and systolic dysfunction. Hypertrophic
cardiomyopathy (B) presents with asymmetric septal hypertrophy.
Constrictive pericarditis (D) presents with pericardial thickening and
calcification.
7. A 62-year-old man with a history of hypertension and diabetes is
prescribed lisinopril. Which of the following is the most important laboratory
value to monitor?
• A. Serum potassium
• B. Serum sodium
• C. Serum calcium
• D. Serum magnesium
Correct Answer: A. Serum potassium
Rationale: ACE inhibitors like lisinopril can cause hyperkalemia by reducing
aldosterone secretion. Serum potassium should be monitored. Sodium (B),
calcium (C), and magnesium (D) are not typically affected.
8. A 35-year-old woman presents with a murmur heard best at the apex,
radiating to the axilla. Which of the following is the most likely diagnosis?
• A. Aortic stenosis
• B. Mitral regurgitation
• C. Mitral stenosis
• D. Aortic regurgitation
Correct Answer: B. Mitral regurgitation
