Might have been because I was dicking about with it that you got those glitches, was trying to absolutely position it to the right of the text because otherwise it kind of pushes the other text left as the size increases. Working fine in Chrome for me.
Like to see bad code?
Here was my original solution.
It is inferior because the heart can stop beating between the “keyframes”, which can result in a sluggish start when resuming the animation. http://codepen.io/jessecfisher/pen/ICfje