How do doctors diagnose if my child has a single ventricle?

Echocardiography. Looking directly at your child's heart with an echocardiogram is a safe, inexpensive and very reliable way of determining if your child has a single ventricle. Physical exam, ecg, chest x-ray and your child's blood oxygen content may make the doctor suspect significant heart disease but echo will allow him to confirm it.
Echocardiogram. If a heart defect is suspected then referral to a cardiologist and echocardiogram (ultrasound) of the hear would be the first step.