Cardiac abnormality seen with Noonan's syndrome is -
Noonan Syndrome :

were previously thought to have a form of Turner syndrome, with which Noonan syndrome shares a number of clinical features.
The observation that patients with Noonan syndrome have normal karyotypes was important in allowing the distinction to be made between the Turner and Noonan syndromes.

Pathophysiology :

The pathophysiology of Noonan syndrome is not fully understood. A disease-causing gene, PTPN11, has been identified. The gene product, SHP2, plays an important role in cardiac semilunar valve development.

Sex :

Noonan syndrome occurs in either a sporadic or autosomal dominant fashion. In either case, males and females are affected equally.

Age :

The disorder is present from birth, but age impacts upon the facial phenotype Infants with Noonan syndrome can be difficult to recognize by facial appearance alone. The phenotype becomes more striking in early childhood, but with advancing age, it may again become quite subtle. Careful examination of an affected child's parents may, in fact, reveal that they are affected mildly.

Clinical features -
Growth parameters

Size at birth is usually within the reference range.
Short stature is present in up to 80% of patients. Average adult height for males is 5'55" and for females is 5'.

Facial features

Triangular-shaped face
Hypertelorism
Down-slanting eyes
Ptosis
Strabismus
Amblyopia
Refractive errors
Low-set ears with thickened helices
High nasal bridge
Short webbed neck

Chest/back features

Pectus carinatum/excavatum
Scoliosis

Cardiac features

The characteristic lesion is a dysplastic/stenotic pulmonic valve, but virtually all types of congenital heart defects have been described in patients with Noonan syndrome.
Hypertrophic cardiomyopathy (obstructive and nonobstructive types) is present in up to 30% of patients.

Abdominal features

Hepatosplenomegaly unrelated to cardiac status is present in approximately 25% of patients.

Genitourinary features 

Renal anomalies are present in 10% of patients but are not clinically significant.
More than half of male patients have undescended testes.

Skeletal features

Joint laxity is present in more than half of patients.
Talipes equinovarus, radioulnar synostosis, cervical spine fusion, and joint contractures are less common findings.

Skin findings 

Lymphedema
Prominent pads of fingers and toes
Follicular keratosis of the face and extensor surfaced
Multiple lentigines

Neurologic findings

Hypotonia
Seizure disorder
Unexplained peripheral neuropathy (infrequent)
VSD
ASD
Pulmonary stenosis
Coarctation of aorta