This Demonstration shows heat flow across a two-dimensional circuit board. A circular heat source of radius 0.0025 meters at a temperature of 80º C radiates heat across a circuit board with an initial temperature of 30º C. This circuit board has a length of 0.20 meters and a width of 0.50 meters. As time approaches infinity, temperature approaches uniformity across the circuit board. Time starts at 2 seconds and ends at 500 seconds. Both a 3D plot and a density plot of the temperature distribution are shown.