Cardiopulmonary resuscitation (CPR) is a common practice in infants and children. Left atrial thrombosis as a complication of chest compressions was not reported; to our knowledge; in premature infants. The patient is a premature female infant (1.3 kg) who was born at 31 week gestation to an HIV positive mother. Initial echocardiogram showed a normal cardiac anatomy and function. The patient was treated with Kaletra for 8 days and a follow up echocardiogram showed a mildly dilated left ventricle with a slight decrease in function. She also had a progressive bradycardia. Kaletra was discontinued but bradycardia deteriorated. At two weeks of age, she developed severe bradycardia and asystole. CPR was performed including chest compressions for 45 minutes in addition to medications and respiratory management. The patient was revived and restored a normal sinus rate and rhythm. An echocardiogram done a few hours later showed a thrombus (4x5 mm in diameter) attached to the left atrial posterior wall. The patient was treated with IV heparin and 5 days later, the echocardiogram was clear of thrombi. Complete and repeated neurological examinations as well as brain MRI and head ultrasound were all normal. Also, there was no evidence of bleeding. We conclude that left atrial thrombi, though rare, are possible complications of prolonged chest compressions in premature infants. We propose performing an echocardiogram in infants surviving prolonged CPR and to early treat any thrombi. Intravenous heparin seems to be safe and effective treatment in that setting.