We compute the time evolution of elliptic flow in non-central relativistic heavy-ion collisions, using a (
e6aa54cfbd364643b678d7de3f2c"" title=""Click to view the MathML source"">2+1)-dimensional code with longitudinal boost-invariance to simulate viscous fluid dynamics in the causal Israel–Stewart formulation. We show that even “minimal” shear viscosity
η/s=/(4π) leads to a large reduction of elliptic flow compared to ideal fluid dynamics, raising questions about the interpretation of recent experimental data from the Relativistic Heavy Ion Collider.