Long-term growth is one of the hardest things for a company to achieve. Countless start-ups emerge, have a good run for a couple of years, and then either get snapped up by a larger company or simply wither on the vine when they can no longer maintain momentum. Given how hard it is to grow consistently for a decade, medical device maker Medtronic's (NYSE:MDT) multi-decade growth record is all the more impressive.

But investing is about the future. Although Medtronic has a 10-year track record of 20% growth, the company is clearly beginning to decelerate a bit. Even management realizes it, as future growth targets are now on the order of 15%.

For Medtronic's third fiscal quarter (ended January), total revenue climbed by 15%, though about 2.5% of that growth came from favorable currency adjustments. Earnings were up a similar 15%, and the firm met Wall Street's expectations.

Sales in cardiac rhythm management, the company's core business, were up 15%, led by the company's strong showing in implantable cardioverter defibrillators (ICDs), up 26%. The spinal business, Medtronic's second-largest segment, also made a strong showing for the quarter, with top-line growth of 23%.

Although the company certainly has opportunities for growth -- in the areas of ICDs, spinal care, diabetes, and perhaps drug-coated stents -- Medtronic will have to fight a bit harder for each dollar. Companies like Guidant (NYSE:GDT) and St. Jude (NYSE:STJ) will continue to hound Medtronic in the ICD business, while many orthopedics companies, including Johnson & Johnson (NYSE:JNJ), want to grow their presence in the spine business. J&J and Boston Scientific (NYSE:BSX), meanwhile, are far ahead of Medtronic in the drug-eluting stent market.

Fortunately, nearly all of Medtronic's targeted markets are growing and likely to continue to do so. The ICD market is growing by more than 20% a year (a blistering pace for a market that is already over $4 billion in size), and markets like vascular care, neurology, spine care, and diabetes are posting solid double-digit growth as well. Even still, the company cannot afford a slip-up. Opportunistic competitors would pounce, and growth would suffer.

Medtronic has a reputation as an "old reliable" of the health-care space, and its valuation reflects it. A trailing price-to-earnings ratio of 29 and an enterprise value-to-free cash flow ratio of 24 are both robust, though not out of line for the industry. The bigger question for Medtronic investors is whether the market will continue to award such a premium for a company that now looks to grow by about 15% a year.

While 15% growth is anything but disgraceful, it would suggest that lower multiples might soon be in order. Long-term investors in Medtronic should do just fine, but anyone considering a quick trade in these shares (something we at the Fool generally discourage) might want to wait for a better price before taking the plunge.

Fool contributor Stephen Simpson, CFA, owns shares of Johnson & Johnson.