Patent foramen ovale (PFO) is a frequent finding in migraine patients. The standard technique for PFO diagnosis is actually trans-oesophageal echocardiography (TEE). It requires the injection of a contrast agent unable to pass the pulmonary filter; hence, it is possible to detect a right-to-left shunt by observing the presence of the contrast medium in the cardiac left compartment. The transcranial Doppler (TCD) device accurately measures the blood flow velocities in different cerebral arteries. It can record microembolic signals (MES) backscattered by microbubbles travelling in the cerebral circulation, and distinguish cardiac shunts from pulmonary shunts. The number of MES is correlated to the entity of the shunt. The near-infrared spectroscopy (NIRS) technique tracks the changes in the concentration of oxygenated and reduced haemoglobin in the brain tissue. PFO is revealed by an alteration of the normal vasoreactivity pattern of the subject during functional stimuli. Magnetic resonance imaging (MRI) provides, at the same time, detailed anatomical information and functional measurements. MRI dynamic perfusion sequences can be used to reliably detect PFO either by visual assessment or by signal-time curves in the pulmonary artery and in the left atrium. A good correlation between TEE and MRI grading scores has been demonstrated, even though the interindividual variability of performing the Valsalva manoeuvre could greatly reduce the sensitivity of the method. Further prospective studies are needed to confirm the PFO MRI grading and to assess the sensitivity and specificity of the method.