public RectangularBorder Border { get; }

Public ReadOnly Property Border As RectangularBorder

using DevExpress.XtraCharts;
using DevExpress.XtraCharts.Heatmap;
using System.Drawing;

namespace HeatmapMatrixAdapterSample {

    public partial class Form1 : Form {
        HeatmapControl heatmap;

        public Form1() {
            InitializeComponent();

            heatmap = new HeatmapControl();
            heatmap.Name = "Heatmap";
            heatmap.Dock = DockStyle.Fill;
            this.Controls.Add(heatmap);

            heatmap.Border.Thickness = 1;
            heatmap.Border.Color = Color.DarkGray;
            heatmap.Border.Visibility = DefaultBoolean.True;

        }
    }
}

Imports DevExpress.XtraCharts
Imports DevExpress.XtraCharts.Heatmap
Imports System.Drawing

Namespace HeatmapMatrixAdapterSample
    Public Partial Class Form1
        Inherits Form

        Private heatmap As HeatmapControl

        Public Sub New()
            InitializeComponent()
            heatmap = New HeatmapControl()
            heatmap.Name = "Heatmap"
            heatmap.Dock = DockStyle.Fill
            Me.Controls.Add(heatmap)
            heatmap.Border.Thickness = 1
            heatmap.Border.Color = Color.DarkGray
            heatmap.Border.Visibility = DefaultBoolean.[True]
        End Sub
    End Class
End Namespace