The 1-Up Heart is an item featured in the first two Super Mario Land games for the original Game Boy. It behaves almost identically to the 1-Up Mushroom, with the only difference being the latter scrolls across the landscape after being unearthed, while the former stays still.
The inclusion of 1-Up Hearts can be attributed to the limited color producing abilities of the Game Boy. Since Super Mushrooms were already present in the game, it would've been hard to distinguish two similar looking mushrooms apart, thus giving birth to the 1-Up Heart. It is also thought that this is why the item never went on to be featured in later Mario series titles, as the 1-Up Mushroom could be easily distinguishable on every later console.
1-Up Hearts can be seen in Balloon Kid, another game on the Game Boy.