Cut paper into a long strip. You can use a large sheet like butcher paper, gift wrap paper or construction paper for a super long heart chain. The length of the strip defines the length of your heart chain while the width determines how tall the hearts will be.
You can also use a smaller sheet of paper (e.g. A4, Letter size, or 9" x 12") to make several heart chains that you can later glue together for a longer chain. I started out with Letter size (8.5" x 11") paper that I halved lengthwise. My two strips are 11" long and 4.25" wide.