Which of the following can be a sign of pneumothorax?

Muffled heart sounds can indicate a pneumothorax in specific situations, especially when it is associated with other conditions such as tension pneumothorax. In tension pneumothorax, air accumulates in the pleural space, increasing intrathoracic pressure which can compress the heart and major vessels, leading to decreased heart sounds upon auscultation. This is a critical sign as it suggests compromised cardiopulmonary function, necessitating immediate medical intervention.

Conversely, options like chest wall symmetry typically signify a normal finding and would not indicate a pneumothorax. Positive transillumination may suggest the presence of fluid or an abnormal structure, while typically positive breath sounds would suggest normal lung function rather than the obstruction or collapse of lung tissue associated with a pneumothorax. Hence, muffled heart sounds are a sound indicator of serious thoracic complications, making it the correct choice in identifying signs of pneumothorax.