<!doctype html>
<html lang="ru">
<head>
<meta charset="utf-8" />
<title></title>
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<style>
.block {
width: 100px;
height: 100px;
background: yellow;
}
</style>
</head>
<body>
<div class="block"></div>
<a href="#" class="link">Link</a>
<script>
$('.link').click(function() {
var div = $('.block');
if( div.innerHeight() == 100 )
div.innerHeight(200);
else
div.innerHeight(100);
});
</script>
</body>
</html>