Dilated cardiomyopathy (DCM) is a clinical diagnosis characterized by left ventricular or biventricular dilation and impaired contraction that is not explained by abnormal loading conditions.(1) Both inherited predisposition and environmental factors play an important part in the natural history of disease.(1) Cardiomyopathies are group of heart diseases that influence cardiac muscles directly and are not related to hypertension, congenital, valvular and pericardial diseases. The most common type of cardiomyopathy is dilated cardiomyopathy (DCM).(2) Definitions of DCM provided by two major professional organizations (American Heart Association (AHA) and European Society of Cardiology (ESC)) Both organizations agreed that DCM could be clinically defined by the presence of left ventricular dilation and contractile dysfunction in the absence of abnormal loading conditions and severe coronary artery disease.(3) Dilated cardiomyopathy usually manifests as chronic systolic heart failure, which is detected by echocardiography as impaired left ventricle fraction shortening less than 28%, with left ventricular end diastolic dimension Z-score>2 ,leading to arrhythmias and sudden death.(4,5) idiopathic dilated cardiomyopathy (DCM) is characterized by dilatation and impaired contraction of the left ventricle or both ventricles, in the absence of underlying causes such as CAD, valve disease, congenital heart disease, or pericardial disease. Most patients present with symptoms of heart failure or arrhythmias, or even sudden cardiac death. An extensive family history (pedigree covering three or four generations), in combination with cardiological screening of first-degree relatives, results in a diagnosis of a familial form of DCM in up to 35% of cases.(11) In a multisite study in the USA and Canada, DCM was the most common form of cardiomyopathy among children (individuals of <18 years of age):66% had idiopathic DCM, whereas of those with DCM due to known causes, 46% had myocarditis and 26% had neuromuscular disease. The annual incidence of DCM in children ranges from 0.18 to 0.73 per 100,000 person-years.(1) Oral PDE5 inhibitors, which primarily include sildenafil, vardenafil ,and tadalafil. Owing to its vasodilation effect and its impact on the endothelial function of blood vessels in the body, it is possible to use them to treat cardiovascular disorders such as pulmonary arterial hypertension and dilated cardiomyopathy. The use of PDE5 inhibitors in HF patients is backed by various theoretical evidence and clinical trials have begun to investigate their potential as an adjunct in the pharmacological management of HF.(6) PDE5 inhibition is an intriguing pharmacological strategy that enhances in vivo NO signaling by increasing the cyclic guanosine monophosphate (cGMP) availability. A number of theoretical backgrounds support the use of PDE5 inhibitors in HF, and several recent clinical studies have tested its clinical viability as a potential adjunct in the pharmacological management of HF.(7) In chronic heart failure improvement in exercise ventilation and aerobic efficiency with sildenafil is sustained and is significantly related with an endothelium-mediated attenuation of exercising muscle over signaling. Chronic sildenafil seems to be a remedy based on CHF pathophysiology and devoid of remarkable adverse effects.(8) Sildenafil is a specific inhibitor of type 5 phosphodiesterase (PDE5) that increases nitric oxide availability and nitric oxide-mediated vasodilation in CHF patients). Interest has therefore been focused on the potential of sildenafil to be beneficial in CHF. In acute studies, sildenafil increased myocardial contractility ,blunted adrenergic stimulation ,reduced left ventricular afterload), and improved lung diffusion capacity ,pulmonary hemodynamics at rest) and on exertion ,and exercise ventilation efficiency and aerobic performance.(8)

Studies with sildenafil in the mdx mouse model support the concept that PDE5 inhibition may have favorable effects to prevent or ameliorate cardiac dys¬function associated with dystrophin deficiency (8, 9). Prophylactic treatment of dogs with golden retriever muscular dystrophy (GRMD) with tadalafil preserved cardiac systolic function, improved measures of circum¬ferential wall strain, and reduced histopathology of car¬diac muscle compared to untreated GRMD animals (9). Congestive heart failure (CHF) occurs when the heart can no longer maintain the baseline metabolic demand triggered by physiological venous pressure. In the pediatric population, it corresponds to a complex entity with multiple etiologies, depending on the age group assessed, being mainly associated with congenital structural malformations, cardiomyopathies, or secondary to arrhythmogenic, infectious, ischemic, toxic or infiltrative events1. cardiomyopathy is the major factor associated with CHF, with a 40% incidence of CHF reported in those patients1. According to Freitas Jr. et al9, the acute administration of sildenafil and sodium nitroprusside has been associated with reverse cardiac remodeling, a reduction in right cardiac chambers and an improvement in biventricular cardiac function9. The use of sildenafil improves oxygen uptake, cardiac index, depression, and quality of life, and reduces aortic stiffness and systemic vascular resistance in patients with CHF.(10)

Inclusion Criteria:- Children from 1-18 year's age, diagnosed primary dilated cardiomyopathy by echocardiography and are admitted at Pediatric Cardiology unit or attend Pediatric Cardiology outpatient clinic in Assiut University children hospital.

• Patient on anti-failure therapy consistent with pediatric heart failure guidelines.

Exclusion Criteria:. Patients less than 1 year old

- Patients with impaired left ventricular systolic function due to other causes like: i. Congenital heart diseases (anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA), severe coarctation of aorta, critical aortic stenosis, metabolic disorders as mitochondrial dysfunction or storage diseases.

ii. Acquired heart diseases as myocarditis, Kawasaki, or arrhythmias

• Post-Operative left ventricular dysfunction
• Known hypersensitivity or contraindications to sildenafil as hypotension (<90/50 mmHg), or severe hepatic/renal impairment or optic neuropathy.

Children aged 1-18 years with a diagnosis of primary dilated cardiomyopathy confirmed by echocardiography, recruited from inpatient and outpatient pediatric cardiology services at Assiut University Children Hospital, Egypt.