public class HeatMapRendererDefinition : RendererDefinition 

{
    string colorBrewerSchemesName = "ArcGIS Colors";
    //Get the style project item that contains the color ramps
    //Refer to the Initialize region for an example of how to get a style item
    //and the color ramp from it.
    //Note: Run within a QueuedTask
    //defining a heatmap renderer that uses values from Population field as the weights
    HeatMapRendererDefinition heatMapDef = new HeatMapRendererDefinition()
    {
        Radius = 20,
        WeightField = "Population",
        ColorRamp = colorRamp,
        RendereringQuality = 8,
        UpperLabel = "High Density",
        LowerLabel = "Low Density"
    };
    CIMHeatMapRenderer heatMapRndr = featureLayer.CreateRenderer(heatMapDef) as CIMHeatMapRenderer;
    featureLayer.SetRenderer(heatMapRndr);
}

/// <summary>
/// Renders a point feature layer using a continuous color gradient to represent density of points.
/// ![Heat map renderer](https://ArcGIS.github.io/arcgis-pro-sdk/images/Renderers/heat-map.png)
/// </summary>
{
  //Check feature layer name
  //Code works with the U.S. Cities feature layer available with the ArcGIS Pro SDK Sample data
  var featureLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>().FirstOrDefault(f => f.Name == "U.S. Cities");
  if (featureLayer == null)
  {
    MessageBox.Show("This renderer works with the U.S. Cities feature layer available with the ArcGIS Pro SDK Sample data", "Data missing");
  }
  //defining a heatmap renderer that uses values from Population field as the weights
  HeatMapRendererDefinition heatMapDef = new HeatMapRendererDefinition()
  {
    Radius = 20,
    WeightField = "NumericField",
    ColorRamp = colorRamp,
    RendereringQuality = 8,
    UpperLabel = "High Density",
    LowerLabel = "Low Density"
  };
  //Note: Run within QueuedTask
  CIMHeatMapRenderer heatMapRndr = (CIMHeatMapRenderer)featureLayer.CreateRenderer(heatMapDef);
  featureLayer.SetRenderer(heatMapRndr);
}