The morphology and extensity of the stenotic lesion is crucial as well as the obstruction ratio. It is well known that the complexity of lesions has a direct impact on endovascular treatment (PTCA/stent); however, the arrangement of the lesions is underestimated and not well studied.We sought to evaluate the haemodynamic effects of different stenotic lesion models and arrangements in vitro.Vascular circulation was simulated in vitro. Oxygenator, tubing set, polytetrahidroflouroethylene synthetic graft, pressure and flow rate, sensors were used to build the simulation model. Measurements of isolated short, isolated long, identical stenotic tandem short, identical stenotic tandem long, sub-critical long, and critical short lesion combinations were performed and haemodynamic parameters were recorded.Tandem lesions were more likely to result in critical stenosis comparing single lesions with the same obstruction ratio. This difference became more significant as the obstruction ratio was raised. Tandem long lesions also resulted in more critical stenosis than tandem short lesions. It can be claimed that tandem lesions can result in more flow restriction with reference to single lesions with the same stenotic ratio. Contrary to expectations, tandem short lesions were found to be more stenotic compared with the same degree long individual lesions.It is effortless to give the decision for simple, discrete and individual lesions, while the ideal decision for long and complicated lesions may remain unclear. Even if these "grey zone" lesions are considered non-critical while investigating them one by one, it must be kept in mind that the overall stenotic effect of these lesions may lead to more haemodynamic impairment.