John, try reversing the stretch to provide strength training for the Heart MMG (meridian muscle group). If that still causes irritation, try stretching and strengthening the
balancing (SI) and
counter-balancing (AP & TH) MMGs.
Generally, try strengthening if you are feeling irritation while stretching a particular MMG, then try stretching and strengthening the balancing and counter-balancing MMGs. Instead of continuing to work on the irritated area, work all of the areas around it. You should not experience pain while stretching if you stick to this method. Also, if you have had any injuries in the area, stick to strength training in order to remove possible scar tissue.