What is the most likely diagnosis for a patient with a visibly depressed sternum and no accompanying symptoms?

The diagnosis of a visibly depressed sternum aligns with the presentation of funnel chest, also known as pectus excavatum. This condition is characterized by a congenital deformity where the sternum is sunken into the chest, resulting in a noticeable indentation. In many cases, it is asymptomatic and discovered incidentally during physical examination or imaging. Since the patient shows no accompanying symptoms, this strongly supports the diagnosis of pectus excavatum, especially when contrasted with other options that typically present with additional clinical findings.

Pneumonia would usually manifest with respiratory symptoms such as cough, fever, or shortness of breath. Asthma is characterized by wheezing, chest tightness, and episodic shortness of breath. Angina pectoris generally involves chest pain that occurs with exertion or stress, often alleviated by rest or nitroglycerin. Given that the patient has no accompanying symptoms, these conditions are less likely.

Thus, the presence of a visibly depressed sternum without any additional symptoms leads to funnel chest being the most appropriate diagnosis.