<div class="row">
    <div class="col-xs-4">
        <div class="block">
            Content for block<br />
            Some more content<br />
            And a bit more<br />
            Last bit
        </div>
    </div>
    <div class="col-xs-8">
        <div class="block">
            Content for block<br />
            Only some more content
        </div>
    </div>
</div>

.row {
  display: table;
  width: 100%; }

.row > div {
  float: none;
  display: table-cell;
  vertical-align: top; }

.block {
  height: 100%;
  background: red; }