Heart words are high frequency words with irregular spelling patterns that must be memorized 'by heart.' However, portions of these words are regular and should be taught as decodable portions. For example: Let's take the word "they." We hear two sounds in this word: /th/ and /ā/. The digraph TH is regular - th says /th/. The irregular portion are the letters EY because it says /ā/. We put a heart over the letters EY because it must be memorized by heart.