Pulmonary arterial hypertension associated with congenital heart disease (PAH-CHD) is one type under group 1 PH. Undiagnosed or delayed diagnosis of significant CHD might lead to significant PAH and at the end might lead to Eisenmenger syndrome. We could expect the degree of PAH in patients with CHD by proper clinical assessment as well as by the basic assessment tools including the chest x-ray (CXR), ECG, and transthoracic echocardiography (TTE). We are presenting a three and half years old child with a delayed/missed diagnosis of large patent ductus arteries (PDA) who present with significant PAH. Clinical evaluation, CXR, ECG, TTE, as well as cardiac catheterization data are presented, with a review of the current guidelines regarding the management of pediatric patients with PAH-CHD.