When sales in the product line responsible for more than half of a huge company's growth come in a little light, you can bet that people are going to notice. Just ask Medtronic (NYSE:MDT).

Revenue for the company's fiscal third quarter grew about 9% (or 12% on a constant currency basis) -- a couple percentage points below the low end of the published analyst range. While the company counterbalanced lower revenue and a lower gross margin elsewhere in the income statement, and delivered earnings in line with analysts' expectations, I'm sure plenty of investors will get twitchy about that revenue shortfall.

The problems started right at the top: ICD revenue grew 21% in the quarter (and accounted for more than half of the company's year-over-year growth), but came in below analysts' projected range. Dovetail that with recent, apparently disappointing ICD numbers from St. Jude (NYSE:STJ), and you now have people wondering whether this golden goose of medical-device growth is getting a little tired.

ICD underperformance isn't my biggest concern, though. I was more interested to see that diabetes revenue grew only 6%, and that revenue from a drug-coated stent (approved and sold outside the U.S.) also seemed a little light. I know that both of these are much smaller businesses relative to ICDs, but if Medtronic wants to balance out its growth, these other units will need to do better.

All in all, though, my basic feelings on Medtronic haven't changed that much. Sure, maybe Boston Scientific (NYSE:BSX) will rejuvenate Guidant (NYSE:GDT). Maybe St. Jude will gain share in neurostimulation. Maybe rivals like Abbott (NYSE:ABT) will be bigger threats in the drug-coated stent and/or diabetes space. But competition was never my primary concern.

Valuation has always been my bigger issue. When there are other high-quality medical device companies out there trading at substantial discounts to fair value, I'm not sure it makes sense to overpay, even for the best of the breed.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).