Transcranial Doppler (TCD) is an ultrasonic technique, mainly used in patients with cerebrovascular disease. Several studies have shown a high prevalence of patent foramen ovale (PFO) with right-to-left shunt (RLS) both in patients with cryptogenic stroke and in healthy subjects. Due to its optimal resolution, transesophageal echocardiography (TEE) is defined the “gold standard” for PFO detection; it is, however, semi-invasive. Nowadays, we need an easier, cheaper and less invasive technique to carry on a PFO screening, particularly in migraine patients, subjects with atrial septal aneurysm, sport divers etc. Transthoracic echocardiography with second harmonic imaging has also been proposed in this clinical setting since its sensitivi ty has been reported simi-lar to that of TEE. TCD is an attractive alternative to TEE in the recognition of a RLS; many papers have pointed out a high concordance between TCD and TEE. Never-theless, TCD accuracy is variable according to protocol and diagnostic criteria. This review is focused on the technical aspects of contrast-enhanced TCD, according to recent recommendations