Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Thoratec (Nasdaq: THOR) shares dropped 14.5% in intraday trading after the medical-device maker released lackluster quarterly results and an uninspiring outlook for this year.

So what: Thoratec's stock price has been on a falling trajectory since October, plunging several times as investors have questioned its product pipeline and mulled competitive concerns regarding its implantable heart pumps. Thoratec's major rival is HeartWare International (Nasdaq: HTWR), which has filed an application with the Food and Drug Administration for a device to challenge Thoratec's HeartMate II.

Now what: Despite the beatdowns administered to Thoratec's stock price over recent months, investing in the company seems risky, especially since its latest quarter shores up the reasoning behind a pessimistic outlook. Thoratec is trading at 15 times forward earnings, but given HeartWare's pending challenge, it may be difficult to achieve forward targets. Investors should count to 10 before pumping cash into Thoratec.

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Alyce Lomax does not own shares of any of the companies mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.