The sweetheart style gets its name from the tapered neck line that creates the shape of a heart with fabric around the bust. The sweetheart neckline is a strapless style that gives a flattering shape to the bust and helps to show off a curvy, feminine silhouette. Sweetheart styles are particularly popular in semi-formal and formal dresses including prom dresses and wedding dresses as they lend themselves particularly well to satin and silk fabrics and long dresses. The sweetheart neckline may appear difficult to sew at first glance but can be hemmed and sewn with a sewing machine in a similar fashion to any other dress neckline.
Draw the shape of two semi-circles or a lower case "m" with your fabric chalk on the front of the dress to create your sweetheart shape. Begin a quarter of the way down the bustier on the left side seam and draw one curve that peaks a quarter of the way across the middle of the dress and ends in the center of the dress one- quarter of the way down the bustier. Draw from the center of the dress, where your last curve ended, upward, to create a second curve that peaks three-quarters of the way across the dress and ends one-quarter of the way down the bustier on the right hand seam. Ensure your two curves are large enough to encase your bust and then incorporate a 1/2-inch margin to allow for a hem.
Trim carefully and precisely around your chalk outline to cut away the excess fabric from the front of the dress.
Turn the dress inside-out.
Fold 1/2 inch of fabric down from the top of the left bust section of the dress to create a smooth curve and pin into place with sewing pins.
Fold 1/2 inch of fabric down from the top of the right bust section of the dress to create a smooth curve and pin into place with sewing pins.
Sew around the semi-circles one at a time with your sewing machine. Begin at the outside of each section and sew inward toward the middle of the dress. Sew slowly and remove the sewing pins as you go.