Background and Purpose. Transcatheter closure of patent fora men ovale (PFO) can benefit from a less invasive diagnostic method than transesophageal echocardiography (TEE). Thirty-three gate power m-mode transcranial Doppler (pmTCD) was evaluated for its accuracy in diagnosis of PFO and utility in evalu ating residual intracardiac right-to-left shunt (RLS) following transcatheter closure. Methods. The sensitivity of pmTCD and single-gate TCD (sgTCD) to detect contrast bubble emboli through RLS was compared during transcatheter PFO closure. During 100 preclosure diagnostic evaluations and in 81 postclosure assessments, embolic tracks on pmTCD were counted following intravenous contrast injections and were graded using a 6-level logarithmic scale. The accuracy of TEE and pmTCD was separately compared to PFO anatomical find ings during transcatheter closures. Results. There were signifi cantly more microemboli detectable on pmTCD (322 ± 166; 95% confidence interval [CI], 388–257) than on sgTCD (186 ± 109; 95% CI, 229-143; P < .001). McNemar change tests sug gest that the diagnostic capabilities of pmTCD and TEE for detecting PFO are comparable and correspond to the anatomi cal findings determined during cardiac catheterization (P= .69 and .45, respectively). During 6-month postclosure evaluation (mean = 185 days), 66% of the patients demonstrated success ful closure without significant RLS (ie, grades 0, I, or II), and 34% were found to have incomplete closure with significant RLS (ie, grades III, IV, or V). Conclusions. pmTCD provides greater sensitivity to contrast bubble emboli than does sgTCD. Among candidates for transcatheter closure, pmTCD provides an improved noninvasive method for diagnosing PFO and evaluating transcatheter closure.