heartbeat is a compound of heart (Old English heorte, from Proto-Germanic *hertô) and beat (Old English bēatan, 'to strike'). Morphologically, the word is best read through the components named in the history, with the modern spelling preserving a compound structure rather than a single unanalyzable stem. In present English, the noun sense is "a single pulsation of the heart; a moment or animating force", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as heart and beat. Its semantic neighborhood includes pulse, pulsation, throb, and beat, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Old English heorte and Proto-Germanic *hertô.