What is HeatMap? Is that an image (array variable) in your program? Or is it a vector (1-D array), since you seem to be using plot() imstead of imshow()?
Anyway, it appears that heatMap is the tag (handle) of an axes control on your GUI, so your plot will plot in that axes. But right after that, you overwrite the axes handle with the handle to the line you just plotted. That makes no sense. Both the line/curve you plotted, and the axes itself, will have their own handle ID number. You don't want to blow away the axes's handle with the handle of the thing you just plotted!
