You can cover the chart do this:

<div class="sameHeight">
    DualChartCard::create(...);
</div>

and adding:

div.sameHieght card-header
{
    height:200px;
}

By this way you can fix the height of all cards.

Let try again this:

div.sameHieght div.card-header
{
    height:200px;
}

You have both class="col-md-4" and class="sameHeight", let try to make it class="col-md-4 sameHeight"

Sorry for my late reply.

Let try this:

div.sameHeight div.card-header,
div.sameHeight div.card-body
{
    height:200px !important;
}

In general, you can use the Inspector tools of browser to view the element and its css class, and then you add to your code the suitable css class rules to tweak the height. Above css can be applied to make height of ChartCard and DualChartCard to be the same.

Let us know if you need further assistance.