How do doctors find out what type of congenital cardiovascular defect kids/people have?

Echocardiogram: If a congenital heart defect is suspected based on symptoms or physical exam findings, an ultrasound machine can be used to visualize the size and shape of the various parts of the heart. This is called an echocardiogram. It can also measure the strength and direction of flow through the various parts of the heart.

Several tests: 1) physical exam and history 2) echocardiogram 3) cardiac catheterization 4) cardiac mri. Any or all of these may be needed to fully delineate a defect, especially when planning surgery. In very small children echo, cardiac cath and MRI may all need to be done with sedation or anesthesia to obtain good results.