The frequency of 18q− is estimated to be approximately 1/40 000 live births and is more commonly associated with certain clinical features including short stature, intellectual disability and malformations of many major organ systems. Congenital cardiac abnormalities are present in 24–36% of cases and screening can prove difficult. A 28-year-old Caucasian female with a history of long arm chromosome 18q deletion was evaluated for persistent dyspnea and decreased activity level. Multiple hospitalizations failed to identify the etiology of her symptoms. Initial transthoracic echocardiogram failed to show any underlying cardiac etiology of her symptoms. Multiple recurrent hospitalizations with the same chief complaint. A transesophageal echo (TEE) showed large secundum atrial septal defect (ASD). Successful surgical closure of her large secundum ASD provided significant symptoms relief. The threshold of obtaining TEE should be low in patients with 18q− which permits early recognition and treatment of underlying structural heart disease.