Key Clinical Findings Analysis

The patient, a 70-year-old male, presents with dyspnoea on exertion. Key physical examination findings include:

• A single second heart sound (S2).
• A loud, diamond-shaped, rough systolic murmur.
• Murmur location: Best heard at the right \(2^{\text{nd}}\) intercostal space.
• Murmur radiation: To the right carotid artery.

Diagnostic Reasoning for Aortic Stenosis

The described clinical features strongly suggest Aortic Stenosis:

• Murmur Characteristics: A loud, rough, diamond-shaped (crescendo-decrescendo) systolic murmur is characteristic of turbulent blood flow across a narrowed aortic valve.
• Location and Radiation: Optimal auscultation in the right \(2^{\text{nd}}\) intercostal space (the aortic area) and radiation to the carotid arteries are classic signs, indicating the murmur originates from the aortic valve and follows the path of blood flow into the aorta.
• Symptoms: Dyspnoea on exertion is a common symptom indicating the heart's inability to meet increased demand due to the stenotic valve.
• S2 Finding: A single S2 can occur when the aortic component is diminished or obscured by the preceding systolic murmur in severe aortic stenosis.
• Age: The patient's age makes degenerative (calcific) aortic stenosis a highly probable cause.

Exclusion of Other Conditions

• Pulmonary Stenosis: Murmur typically heard at the left upper sternal border, radiating differently.
• Ventricular Septal Defect (VSD): Murmur usually located at the left lower sternal border, without carotid radiation.
• Patent Ductus Arteriosus (PDA): Characterized by a continuous murmur, not systolic.

Likely Diagnosis

The combination of murmur location, radiation, timing, quality, associated symptoms, and patient demographics overwhelmingly supports Aortic Stenosis as the diagnosis.