Just a Little Mistake $20.00 Inside Message Blank Inside Packages of Heartstrings® cards are shrink-wrapped and sold in sets of 10 cards with envelopes. The actual card size is 4 1/4" x 5 1/2". Just a Little Mistake quantity Add to cart SKU: 468. Categories: Baby - Parenting, Sympathy - Healing. Related Products A Big Addition $20.00 Acute Pain $20.00 We all Swim Upstream $20.00 The Plot Thickens $20.00