Can a cardiologist diagnose a murmur as innocent just by listening?

Murmur: A cardiologist well trained in physical diagnosis can generally make a high probability determination of no significant hemodynamic problem by examination.

Usually: A murmur is just an extra sound heard when listening to the heart. Some murmurs are innocent, but other murmurs may be caused by a structural heart problem, such as a septal defect (hole between the sides of the heart), valvular heart disease (a tight or leaky valve) or a tight blood vessel. Innocent murmurs typically sound different, but we will often do an echo (or ultrasound) to double check.

Certainly: The experience and training they have places their ability to decide which of these need extra studies and which do not. The same goes for a well trained pediatrician or family practice doc. If you are in a setting where additional studies are ordered every time a symptom appears, they are either poorly trained, substituting studies for experience, doing them to fatten the bill or avoid lawsuits.