A 74-year-old man presented to the ER complaining of chest pain that is increasing in frequency, duration, and intensity. He also has shortness of breath. He is given nitroglycerin in the ER and still has chest pain. What is the most likely diagnosis?

Correct Answer: D

Rationale: Persistent pain despite nitroglycerin suggests unstable angina.

Correct Answer: C

Rationale: Ventricular septal defect (VSD) is the most common congenital heart defect causing an initial left-to-right shunt due to higher left ventricular pressure.

Correct Answer: D

Rationale: Byssinosis, caused by cotton dust exposure, is a hypersensitivity pneumonitis seen in textile workers.

Correct Answer: C

Rationale: The human heart has four valves: tricuspid, pulmonary, mitral, and aortic.

Correct Answer: B

Rationale: Levels above this range increase the risk of toxicity.