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

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.
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.

Related Questions

Do babies always die if a congenital heart problem?

Not as likely today. Remarkable improvements in pre-delivery diagnosis and after birth interventions have made congenital heart problems much more manageable today. With newer technology, a heart defect can often be noted before delivery, then you probably will be advised to deliver at a hospital with a dedicated pediatric cardiology team on standby. There life-saving surgery or medication can be given immediately. Read more...
No. In fact, most babies with congenital heart disease are expected to reach adulthood. Some of the more severe lesions have up to a 30% mortality in the first year, however these are less common than the more treatable defects. Read more...