What: Shares of medical device manufacturer Thoratec (Nasdaq: THOR) shrugged off the market's big decline today and rose as much as 17% on higher-than-average volume.

So what: After the market closed on Friday, Thoratec competitor HeartWare (Nasdaq: HTWR) disclosed data that showed patients using its circulatory-support device had a 9.2% chance of forming blood clots. This compares with a 3% rate with Thoratec's HeartMate II. While experts don't seem to think that this will prevent HeartWare from getting its device approved in the U.S., it could delay the approval for bridge-to-transplant use and make an approval for destination therapy more difficult.

Now what: For obvious reasons, this is all potentially good news for Thoratec, as it may now have more time to build the HeartMate II's footprint before it has to deal with competition from HeartWare. Wall Street also helped bolster the excitement today as an analyst at Lazard noted that it increased its pump-sales forecast for Thoratec, while an analyst at Leerink Swann boosted the company's shares to "outperform."

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Fool contributor Matt Koppenheffer does not have a financial interest in any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.