When there is erectile dysfunction in individuals who appear to be healthy, dynamic penile Colour Doppler Ultrasound is an extremely useful diagnostic examination. In fact, thanks to the differentiation of the colour of venous (blue) and arterial (red) blood, the specialist doctor can see and analyse the blood flow within the cavernous bodies of the penis. The dynamic form of the examination involves the painless injection, using ultra-thin needles directly into the penis, of local vasodilator drugs. This allows the flow of blood and the successful completion of the analysis.