<div class="your_slider_block">
...text...
<div class="your_hided_block">Скрытый контент</div>
</div>
.your_hided_block {
overflow: hidden;
height: 0;
transition: height .25s;
}
.your_slider_block:hover .your_hided_block {
height: 100px; /* Нужная высота блока */
}