objective. Simple diagnostic techniques such as contrast transcranial Doppler sonography (cTCDS) are popular for assessing a right-to-left shunt (RLS) because of their high sensitivity In this study, we applied cTCDS to a large patient group with a patent foramen ovale, proved by contrast transesophageal echocardiography (TEE). Methods. One hundred one patients with stroke, in whom a patent RLS had been shown on contrast TEE, were investigated by TCDS of both middle cerebral arteries. Injection of 10 mL of agitated saline was applied without and subsequently with the Valsalva maneuver (VM) at the beginning of the contrast agent injection, and then 10 mL of a galacto,se-based contrast agent was applied in the same protocol. Results. In all patients, cTCDS with the galactose contrast agent showed an RLS when performed with VM, but it showed an RLS in only 59 patients without VM. In contrast, saline showed an RLS in 54 patients with VM and in 20 patients without VM. The differences in diagnostic sensitivity were statistically significant (P < .001). Eighteen patients had only 1 microembolic signal (MES) after galactose injection, whereas others had more. The mean (SD) arrival times of the MES were 9 (6) seconds (range, 1-51 seconds) after galactose injection with VM and 9 (3) seconds (range, 2-20 seconds) after agitated saline with VM. The differences were not significant. Conclusions. Contrast TCDS with VM shows a TEE-proven RLS with 100% sensitivity, but this was not true with galactose application without VM or agitated saline with or without VM. Therefore, use of the galactose contrast agent with VM is strongly recommended for detecting an RLS on TCDS. However, the arrival time and number of MESs detected need to be tested further.