How to diagnose Congenital Heart Defects ? 

Severe congenital heart defects generally are diagnosed during pregnancy or soon after birth. Less severe defects often aren't diagnosed until children are older.
                
Minor defects often have no signs or symptoms. Doctors may diagnose them based on results from a physical exam and tests done for another reason.
                
Specialists Involved
                
Pediatric cardiologists are doctors who specialize in the care of babies and children who have heart problems. Cardiac surgeons are specialists who repair heart defects using surgery.
                
Physical Exam
                
During a physical exam, the doctor will:
                
Listen to your child's heart and lungs with a stethoscope
                
Look for signs of a heart defect, such as cyanosis (a bluish tint to the skin, lips, or fingernails), shortness of breath, rapid breathing, delayed growth, or signs of heart failure
                
Diagnostic Tests
                
Echocardiography
                
Echocardiography (echo) is a painless test that uses sound waves to create a moving picture of the heart. During the test, the sound waves (called ultrasound) bounce off the structures of the heart. A computer converts the sound waves into pictures on a screen.
                
Echo allows the doctor to clearly see any problem with the way the heart is formed or the way it's working.
                
Echo is an important test for both diagnosing a heart problem and following the problem over time. The test can show problems with the heart's structure and how the heart is reacting to those problems. Echo will help your child's cardiologist decide if and when treatment is needed.
                
During pregnancy, if your doctor suspects that your baby has a congenital heart defect, fetal echo can be done. This test uses sound waves to create a picture of the baby's heart while the baby is still in the womb.
                
Fetal echo usually is done at about 18 to 22 weeks of pregnancy. If your child is diagnosed with a congenital heart defect before birth, your doctor can plan treatment before the baby is born.
                
EKG (Electrocardiogram)
                
An EKG is a simple, painless test that records the heart's electrical activity. The test shows how fast the heart is beating and its rhythm (steady or irregular). An EKG also records the strength and timing of electrical signals as they pass through the heart.
                
An EKG can detect if one of the heart's chambers is enlarged, which can help diagnose a heart problem.
                
Chest X Ray
                
A chest x ray is a painless test that creates pictures of the structures in the chest, such as the heart and lungs. This test can show whether the heart is enlarged. It also can show whether the lungs have extra blood flow or extra fluid, a sign of heart failure.
                
Pulse Oximetry
                
For this test, a small sensor is attached to a finger or toe (like an adhesive bandage). The sensor gives an estimate of how much oxygen is in the blood.
                
Cardiac Catheterization
                
During cardiac catheterization (KATH-e-ter-ih-ZA-shun), a thin, flexible tube called a catheter is put into a vein in the arm, groin (upper thigh), or neck. The tube is threaded to the heart.
                
Special dye is injected through the catheter into a blood vessel or one of the hearts chambers. The dye allows the doctor to see blood flowing through the heart and blood vessels on an x-ray image.
                
The doctor also can use cardiac catheterization to measure the pressure and oxygen level inside the heart chambers and blood vessels. This can help the doctor figure out whether blood is mixing between the two sides of the heart.
                
Cardiac catheterization also is used to repair some heart defects.