How to center text vertically in a heading?

I have a h1 element that has width and height set. I want to vertically center the text but I can't seem to do it. Please see my code below:

Fiddle

h1 {
  width: 150px;
  height: 150px;
  background-color: #888888;
  color: white;
  text-align: center;
  vertical-align: middle;
}

<h1>Test</h1>