HCA (NYSE:HCA) gave hospital investors a bit of a surprise today by pre-releasing second quarter results.

Those results impressed investors, sending shares skyrocketing by nearly 10%, but it wasn't just HCA that headed higher. Competitors including Tenet Healthcare (NYSE:THC) jumped too. 

HCA Chart

HCA data by YCharts

In the following slideshow you'll learn what was behind HCA's shocking quarter and what you might expect from here.