Cardiac malformations can be very dangerous. Commonly, in adults, cardiac malformations can manifest as coronary-pulmonary artery fistulas, which are characterized by ischemia of the coronary arteries, and the patient will progressively develop pulmonary hypertension as well as myocardial changes caused by ischemia of the coronary arteries, which can lead to heart failure. Other cardiac malformations, such as tetralogy of Fallot or severe atrial septal defects or ventricular septal defects in pediatric patients, may lead to early death due to untreated severe heart failure. If left untreated for a long time, an untreated arterial duct can end up with heart failure due to changes in the heart muscle as well as the blood vessels in the lungs. This is why it is still important to treat heart malformations once they are detected if there are very good treatment options available.