Abstract: AIM: To compare the abilities of transesophageal echocardiography(TEE) and contrast transcranial Doppler(cTCD) to detect a right-to-left shunt(RLS) and small patent foramen ovale(PFO).METHODS: A total of 32 patients(18 males and 14 females) ages 16 to 52 years(mean 35.4±14.6) years with small PFO were evaluated.Among the patients,21cases were due to cryptogenic stroke,five cases to transient ischemic attack and five cases were attributable to migraine.Cryptogenic stroke with infarcted lesions was confirmed by CT or MRI without other identifiable causes such as aorta and cerebral vascular disease or left ventricular system disease.Average diameter of PFO was <2 mm,and atrial septum aneurysm may not be identified.RESULTS: Average diameter of PFO in 32 patients was 0.6-2.0 mm(1.4±0.5) mm by TEE without RLS by color Doppler.Degree of RLS was evaluated by cTCD and included four cases(12.5%) of grade I,11 cases(34.4%) of grade II,nine cases(28.2%) of grade III and eight cases(25%) of grade IV.In all cases,4/32 cases(12.5%) were without RLS,20 cases(62.5%) with RLS after Valsalva maneuver and eight cases(25%) with RLS at rest.In 32 patients there were 28 cases of transcatheter closure treatment in which cTCD III in >17 cases were successfully completed interventional therapy.Mean operative time was(23.5±7.3) min.In five patients with cTCD level II,<10 microemboli signals did not have successful closure.Six cases of 10-20 microemboli signals were successfully occluded,but the average operative time was(65.5±18.4) min,obviously longer than in the cTCD level III group(P<0.01).CONCLUSIONS: Simultaneous determination of the PFO size and RLS volume is needed in order to accurately reflect the clinical status of the PFO paradoxical embolism.