SVG example: lines_with_arrow

<svg width="400" height="200" xmlns="http://www.w3.org/2000/svg">

    <marker id="triangle"
      viewBox="0 0 10 10"
      refX="0"
      refY="5" 
      markerUnits="strokeWidth"
      markerWidth="4"
      markerHeight="3"
      orient="auto">

      <path d="M 0 0 L 10 5 L 0 10 z" />

    </marker>

	<line         x1=" 100" y1="50.5" x2="300" y2="50.5" marker-end="url(#triangle)" stroke="black" stroke-width= "7"/>
	<polyline points=" 100     100        300      100"  marker-end="url(#triangle)" stroke="red"   stroke-width="10"/>
	<path          d="M100     150.5     l200        0"  marker-end="url(#triangle)" stroke="blue"  stroke-width="13"/>

</svg>