A cardiac cath is done when a sheath is inserted into the thigh of the patient and a catheter is threaded through. This will be placed in a vein and an artery simultaneously so they can measure the body pressure at the same time as the pulmonary and cardiac pressure. This is because an infant’s body pressure is much lower than an adults, so a ratio is taken rather than the actual pressure. The pulmonary pressure should normally be less than half of the body pressure. The catheter in the artery is threaded up to the heart and the pressure in the four chambers is measured under baseline. Then a medication is introduced that will increase the cardiac output. In a normal heart, the vessels will dilate with the increased blood flow and the pressure will only increase minimally. This pressure is them measured in all chambers.Finally, while the cardiac output is high, nitric oxide is introduced. The nitric oxide is a medication that will dilate the vessels and alleviate the increased pressure. This is to mimic the effects of Sildenafil (Viagra, Ravatio) which is traditionally given to patients with pulmonary hypertension. The Sildenafil delays the breakdown of nitric oxide in the body and allows for the effects of this natural vasodilator to stay around a little longer and decrease the pulmonary hypertension. The pressures are then measured and compared to the baseline pressures.