When the rivet is released within {TAIL ~ an artificial fistula} formed through the aorta and vena cava walls, it expands to trap the walls between {HEAD ~ the two expanded heads} 
When the rivet is released within { TAIL ~ an artificial fistula } formed through the aorta and vena cava walls , it expands to trap the walls between { HEAD ~ the two expanded heads }
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD