Congenital left atrial appendage aneurysm are a rare entities and are caused by congenital dysplasia of the atrial muscle. Less than 100 cases have been reported in literature so far. Patients usually present with dyspnoea ,palpitations ,thromboembolic phenomenon in their 3rd decade with slight higher preponderance in females.In asymptomatic individuals the condition is often diagnosed incidentally during cardiac imaging . We hereby report a case of 30 year old male with a giant LAAA containing thrombus presenting with palpitations diagnosed with echocardiography and cardiac MRI. The patient successfully underwent aneurysmal resection sugery, post which atrial arrhthias stopped and symptoms relieved. Therefore,even though rare,if a young patient presents with atrial tachyarrthymia with no other associated cardiac pathologies, a LAAA should be ruled out. Since this condition has been shown to be associated with increased morbidity and mortality. A transthoracic echocardiogram or even better,a TEE colour Doppler echocardiogram may suggest the diagnosis by demonstrating the exchange of blood between LA and LAAA. Surgical resection is the standard modalitiy of treatment even in asymptomatic individuals to reduce risk of associated complications. Learning objectives : It is a rare case of giant left atrial appendage aneurysm, few cases have been reported, LA appendage aneurysm usually present as atrial arrhythmias ,stroke or as incidental diagnosis on imaging.Though patients may be asymptomatic it still requires operative intervention since it has very high risk of atrial arrhythmias and thrombus formation which result into stroke.Therefore, if a young patient presents with atrial tachyarrthymia with no other cardiac pathologies, LAAA should be ruled out.