yo creo que no lo estabas poniendo bien, yo probe un codigo y si me sirvio, prueba el codigo ;)
Código HTML:
Ver original<!DOCTYPE html>
#container {
margin: 20px;
width: 200px;
height: 200px;
}
<svg xmlns="http://www.w3.org/2000/svg" version="1.1" x="0px" y="0px" viewBox="0 0 100 100">
<path fill-opacity="0" stroke-width="1" stroke="#bbb" d="M81.495,13.923c-11.368-5.261-26.234-0.311-31.489,11.032C44.74,13.612,29.879,8.657,18.511,13.923 C6.402,19.539,0.613,33.883,10.175,50.804c6.792,12.04,18.826,21.111,39.831,37.379c20.993-16.268,33.033-25.344,39.819-37.379 C99.387,33.883,93.598,19.539,81.495,13.923z"
/>
<path id="heart-path" fill-opacity="0" stroke-width="3" stroke="#ED6A5A" d="M81.495,13.923c-11.368-5.261-26.234-0.311-31.489,11.032C44.74,13.612,29.879,8.657,18.511,13.923 C6.402,19.539,0.613,33.883,10.175,50.804c6.792,12.04,18.826,21.111,39.831,37.379c20.993-16.268,33.033-25.344,39.819-37.379 C99.387,33.883,93.598,19.539,81.495,13.923z"
/>
</svg>
<script src="https://rawgit.com/kimmobrunfeldt/progressbar.js/1.0.0/dist/progressbar.js"></script> <script type="text/javascript"> // Docs: http://progressbarjs.readthedocs.org/en/1.0.0/
var bar = new ProgressBar.Path('#heart-path', {
easing: 'easeInOut',
duration: 1400
});
bar.set(0);
bar.animate(1.0); // Number from 0.0 to 1.0