Hi, Mattica:
     You can try the following OC code:
#define	STR_HEATMAP_TEMPLATE	"heatmap.otp"
void	test_CreateHeatMap()
{
	//create graph from template and get first layer to add plot
	GraphPage gp;
	gp.Create(STR_HEATMAP_TEMPLATE);
	GraphLayer gl = gp.Layers(0);
	//prepare data for plot
	MatrixLayer ml("[MBook1]");
	MatrixObject mo(ml, 0);
	//plot data on graph layer.
	gl.AddPlot(mo, IDM_PLOT_CONTOUR);
	return;
}