public class HeatMapRendererDefinition : RendererDefinition 

string colorBrewerSchemesName = "ArcGIS Colors";
StyleProjectItem style = Project.Current.GetItems<StyleProjectItem>().First(s => s.Name == colorBrewerSchemesName);
string colorRampName = "Heat Map 4 - Semitransparent";
IList<ColorRampStyleItem> colorRampList = await QueuedTask.Run(() =>
{
    return style.SearchColorRamps(colorRampName);
});
ColorRampStyleItem colorRamp = colorRampList[0];

await QueuedTask.Run(() =>
{
    //defining a heatmap renderer that uses values from Population field as the weights
    HeatMapRendererDefinition heatMapDef = new HeatMapRendererDefinition()
    {
        Radius = 20,
        WeightField = "Population",
        ColorRamp = colorRamp.ColorRamp,
        RendereringQuality = 8,
        UpperLabel = "High Density",
        LowerLabel = "Low Density"
    };

    FeatureLayer flyr = MapView.Active.Map.Layers[0] as FeatureLayer;
    CIMHeatMapRenderer heatMapRndr = (CIMHeatMapRenderer)flyr.CreateRenderer(heatMapDef);
    flyr.SetRenderer(heatMapRndr);
});