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: Shares of Volcano (NASDAQ:VOLC), a company that makes precision-guided medical devices to aid in diagnosing coronary and peripheral vascular diseases, fell as much as 20% after updating its third-quarter, full-year, and 2014 revenue guidance below the current Wall Street consensus.

So what: According to Volcano's press release, the company delivered just a 2.2% increase in sales for the third quarter to $95.8 million. Volcano's management notes that while its intravascular imaging and fractional flow reserve segments performed well, a negative foreign exchange impact of $5.4 million and weak PCI sales in the U.S. hurt its results. Wall Street had expected $97.1 million in sales this quarter. For the full year, Volcano pitted its forecast at $391 million to $395 million, which is also below the $398.7 million that analysts expected. Finally, as icing on the cake, Volcano projected revenue growth of 9% to 11% in fiscal 2014, which at the midpoint of its 2013 guidance would be $428 million to $436 million -- also below the $442 million the Street was looking for. On the heels of this update, JPMorgan Chase, Credit Suisse and Canaccord Genuity all downgraded Volcano.

Now what: I'm in both a forgiving and unforgiving mood given today's revenue update. On one hand, I can understand that Volcano has little control over its foreign exchange pressures, and I'm willing to absolve its third-quarter miss on that accord. However, weakness in product sales in the U.S. moving forward is a completely different story when the company is essentially hugging the profitability flat-line. This is a case where the products are certainly exciting, and I can see Obamacare potentially leading to more preventative treatments that incorporate Volcano's tools; but the promise hasn't translated into consistent profits. Until such time as that happens, I'd simply prefer to stick to the sidelines.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

The Motley Fool owns shares of JPMorgan Chase and recommends Volcano. 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.