Abstract: AIM To assess right to left shunt of patent foramen ovale (PFO) by transthoracic echocardiography (TTE) combined with right heart contrast echocardiography by chest (cTTE) in unexplained cerebral infarction patients. METHODSWe chose 285 unexplained cerebral infarction patients as observation group and 114 healthy subjects as controls. All subjects underwent TTE and then cTTE activated by ASB and atmosphere. The right to left shunt and the shunt grade were evaluated. RESULTSThe positive rate of right to left shunt in observation group and control group was 51% and 32%, respectively, with significant difference by statistical analysis (P<0.01). The positive rates of small, medium and large shunt in observation group and control group were, respectively, 14% vs. 10%, 6% vs. 3% and 31% vs. 19%. There was no statistical significance in small and medium shunt but there was a statistical difference (P<0.01) in large shunt between observation group and control group. CONCLUSIONRight to left shunt in unexplained cerebral infarction patients is significantly higher than in healthy subjects, indicating right to left shunt of PFO may be one of the core causes for cerebral infarction. cTTE is an effective method to examine right to left shunt in the unexplained cerebral infarction patients.