BACKGROUND: Paradoxical thrombotic embolism via right-to-left shunt is a risk factor for ischemic stroke, especially in younger subjects. Transtemporal Doppler shows a sensibility and specificity in the detection of patent foramen ovale comparable to that of transesophageal echocardiography, but even younger patients may not have a sufficient acoustic temporal bone window (up to 10%). METHODS AND RESULTS: We thus studied prospectively in 74 patients subsequent to a recent stroke of undetermined origin whether transforaminal (foramen magnum) Doppler is an alternative to transtemporal Doppler in the detection and quantification of right-to-left cardiac shunt. We found a highly significant correlation between the two methods. CONCLUSIONS: We conclude that transforaminal Doppler may be a complement and alternative to transtemporal Doppler and thus improve its value as a screening method for right-to-left cardiac shunt due to patent foramen ovale.