Its pretty simple. I'll explain but I'll also give yuo a link to a more visual descritption(pictures are good!)
Take your silk and fold it in half. Wet it slightly with a mister(enough so the 2 layers stay together). Draw half a heart along the fold. I have found that my daughter's washable markers work well for marking silk/fabric for tieing and dyeing. Anyways...beginning at the bottom point of the heart, accordian fold along the line that you have drawn. As you get up to the rounded "hump" of the heart you might have to take a bit more care to get the drawn lines to match up into a straight line in the folds.
When you have it folded, bind the piece along the straight line that has formed along the fold. I also like to go out a little from this line and bind a second time.Tie-dyed.com
also has a got visual tutorial on folding a heart.
FYI-To other dyers, it appears that Fiber-arts.com, a great resource for us dyers and fiber artists will be coming back online at the beginning of March. Another new resource iTiedye.com
should be going live this coming week.
Mods...hope it is o.k. to mention these becuase they are great informational resources for dyers/fiber-artists(and I have no economic connection to either, just love great resources