Use a different tool, or isolate the artefact. For the second selection, make a rough selection of the artefact and any area from which you are happy to used as source pixels, and copy to a new layer. Then use the healing brush on that layer. It will then not be able to substitute one bad area for another.
But I would probably use the Patch tool when working close to an edge. Make your selection overlap the edge to include both the arm and white background (as per the image) and slide along to a nice clean area of the arm. In the example I addapted from your screen grab, there would be a problem because the area you want to toutch up extends beyond the image boundry, and you would need to inlude that in your initial selection.
thnak you, good suggetion!