The invention relates to an assistance device, an assistance system and an assistance method for assisting a practitioner in an interventional hemodynamic (e.g fractional flow reserve (FFR)) measurement on a subject. The FFR pressure measurements are combined with an, for example, angiography-based assessment of the coronary vessel geometry. An advanced computational fluid dynamics model may be employed to add flow and myocardial resistance data based on the interventional pressure values and on a vascular model generated prior to the intervention. In case that these data are available prior to the intervention, the location of most optimal positions for pressure measurements can be pre-calculated and by overlay of the vessel tree, for example, on the X-ray projection, advice can be given for the interventional cardiologist during the intervention.