How soon can you tell if a new baby has a heart problem like wolff parkinson syndrome?

Newborn or later: Of the two i've seen in 3 decades, one was picked up in the newborn nursery due to a rapid pulse during vital sign check & one came in at a few months of age as a gray baby (tachycardia related). Both did quite well with rx. As a rare process, it is likely not to show up until the abnormal rate is detected & an ekg is done.

EKG: There are many different kinds of heart problems, of which WPW is one. Most heart problems will require evaluation such as ekg, echocardiogram and physical exam to diagnose.