This is a medical question of type : exams and tests 
 How to diagnose Tetralogy of Fallot ? 
 Doctors diagnose tetralogy of Fallot based on a baby's signs and symptoms, a physical exam, and the results from tests and procedures.
                
Signs and symptoms of the heart defect usually occur during the first weeks of life. Your infant's doctor may notice signs or symptoms during a routine checkup. Some parents also notice cyanosis or poor feeding and bring the baby to the doctor. (Cyanosis is a bluish tint to the skin, lips, and fingernails.)
                
Specialists Involved
                
If your child has tetralogy of Fallot, a pediatric cardiologist and pediatric cardiac surgeon may be involved in his or her care.
                
A pediatric cardiologist is a doctor who specializes in diagnosing and treating heart problems in children. Pediatric cardiac surgeons repair children's heart defects using surgery.
                
Physical Exam
                
During a physical exam, the doctor may:
                
Listen to your baby's heart and lungs with a stethoscope.
                
Look for signs of a heart defect, such as a bluish tint to the skin, lips, or fingernails and rapid breathing.
                
Look at your baby's general appearance. Some children who have tetralogy of Fallot also have DiGeorge syndrome. This syndrome causes characteristic facial traits, such as wide-set eyes.
                
Diagnostic Tests and Procedures
                
Your child's doctor may recommend several tests to diagnose tetralogy of Fallot. These tests can provide information about the four heart defects that occur in tetralogy of Fallot and how serious they are.
                
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 diagnosing tetralogy of Fallot because it shows the four heart defects and how the heart is responding to them. This test helps the cardiologist decide when to repair the defects and what type of surgery to use.
                
Echo also is used to check a child's condition over time, after the defects have been repaired.
                
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.
                
This test can help the doctor find out whether your child's right ventricle is enlarged (ventricular hypertrophy).
                
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 or 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-eh-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 heart's chambers. The dye allows the doctor to see the flow of blood 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.