A transient thermal imaging technique is used to monitor heat diffusion at the surface of the antiferromagnetic spin ladder material Ca9La5Cu24O41. This material shows highly anisotropic thermal conductivity due to a large uni-directional magnetic heat transport along the ladders. The thermal conductivity is measured using optical heating as well as electrical heating, yielding 37 +/- 3W m(-1) K-1 for the fast (ladder) direction and 2.5 +/- 0.5W m K-1 for the slow direction, respectively. The fast direction result is in agreement with the thermal conductivity measured using other dynamic methods, but about 60% lower than the thermal conductivity measured using steady state methods. (C) 2012 Elsevier Ltd. All rights reserved.