There is a chance to receive 25 Heart of ice tokens from combat drops or skilling while the amulet is equipped. After receiving the tokens, the amulet will lose 25 charges and a message will be displayed which reads: Your heartfreezer amulet feels colder for a moment, and you collect 25 Heart of Ice tokens. If it activates while you have a full inventory, it'll show the message: "Your heartfreezer amulet feels colder for a moment, but you don't have the space for any Hearts of Ice tokens in your inventory." and will retain its charge.