The imagesc demo in this answer produces a plot nearly identical to a heatmap and the last line allows you for format the cell labels.
Example of setting cell labels (adaptation of the last line from that answer),
th = text(xTxt(:), yTxt(:), labels(:), ...
'VerticalAlignment', 'middle','HorizontalAlignment','Center',...
'FontSize', 12, 'FontWeight','bold','Color','g');
