[Target Subject]: Cardiology / Pathology [Key Concepts]: Aortic Stenosis presentation and pathophysiology [Paste Source Text Here]: Aortic stenosis (AS) is characterized by narrowing of the aortic valve orifice. The classic clinical triad of symptoms includes Dyspnea, Angina, and Syncope (often remembered by the mnemonic SAD). On physical exam, it presents with a crescendo-decrescendo systolic ejection murmur, best heard at the right upper sternal border, radiating to the carotids. A key feature is 'pulsus parvus et tardus'—pulses are weak and delayed. The most common cause in older patients (>70) is calcification, whereas in younger patients (<60) it is typically due to a bicuspid aortic valve. [Target Knowledge Level - e.g., Beginner, Advanced, Exam Prep]: USMLE Step 1 Exam Prep [Preferred Flashcard Structure - e.g., Concept-Descriptor, Cloze Deletions, Mixed Question-Answer]: Mixed Question-Answer and Cloze Deletions