 Lung AVMs may be suspected because of the abnormal appearance of the lungs on a chest X @-@ ray , or hypoxia ( low oxygen levels ) on pulse oximetry or arterial blood gas determination . Bubble contrast echocardiography ( bubble echo ) may be used as a screening tool to identify abnormal connections between the lung arteries and veins . This involves the injection of agitated saline into a vein , followed by ultrasound @-@ based imaging of the heart . Normally , the lungs remove small air bubbles from the circulation , and they are therefore only seen in the right atrium and the right ventricle . If an AVM is present , bubbles appear in the left atrium and left ventricle , usually 3 – 10 cardiac cycles after the right side ; this is slower than in heart defects , in which there are direct connections between the right and left side of the heart . A larger number of bubbles is more likely to indicate the presence of an AVM . Bubble echo is not a perfect screening tool as it can miss smaller AVMs and does not identify the site of AVMs . Often contrast @-@ enhanced computed tomography ( CT angiography ) is used to identify lung lesions ; this modality has a sensitivity of over 90 % . It may be possible to omit contrast administration on modern CT scanners . Echocardiography is also used if there is a suspicion of pulmonary hypertension or high @-@ output cardiac failure due to large liver lesions , sometimes followed by cardiac catheterization to measure the pressures inside the various chambers of the heart . 
