The effect of different percentages of coil mesh in a cerebral aneurysm on the pulsatile flow and pressure in the parent vessel and aneurysm lumen was evaluated. Geometric data on a basilar tip aneurysm and vertebrobasilar arteries after subarachnoid hemorrhage was obtained by computer tomographic angiography. Intraarterial pressure was measured at four vertebrobasilar points before and after treatment with detachable coils. Pulsatile flow was documented by transcranial ultrasonography. A three-dimensional computer simulation was created using a commercial fluid dynamics solver for four aneurysm conditions: (1) before intervention; (2) with a 20% filling showing a complete cessation of the inflow through the aneurysm neck; (3) with a 12% filling showing an incomplete deceleration of inflow through the aneurysm neck, with a remaining flow around the embedded platinum coils; and (4) with a 12% filling and simulation of clotted aneurysm dome, which did not inhibit persisting flow phenomena. The relative pressure amplitudes neither increased nor decreased under the different simulated aneurysm filling conditions. Inserted platinum coils can immediately and decisively relieve the influx of pulsating blood and allow for initial clotting. To reach this effect, a volume density of 20% platinum coil mesh in the aneurysm neck is needed.