Feeling your heart race isn't always the wonderful experience poets write about. Sometimes it can be downright deadly. Selling products to combat those deadly heart problems helped propel fourth-quarter sales growth at St. Jude Medical (NYSE:STJ) to the tune of 18% over the prior quarter. While the stock has retraced almost half of its gains from a mid-2004 low, the business is still growing at a heart-thumping pace.

Sales for ICDs (that's implantable cardioverter defibrillators) were up 63% in the fourth quarter as the company continues to gain market share. While St. Jude has other good businesses that sell important products such as electrophysiology catheters and artificial heart valves, ICD sales are the real story; they represented more than 70% of the company's growth. What's more, the ICD market is worth at least $4 billion, and it's growing at roughly 20% a year -- a phenomenal growth rate for a market already so large.

Once used primarily to treat patients with a history of tachycardia (that's a too-fast heart rate), ICDs are increasingly being explored as a treatment for congestive heart failure -- a grievous medical condition that affects at least 5 million people in the U.S. alone. This expansion into congestive heart failure has also been important for St. Jude, since much of the company's growth has come from new high-voltage devices labeled to treat this condition. As evidence continues to mount that more patients could benefit from these devices, growth should continue at a healthy clip for at least a few more years, if not longer.

While St. Jude has come on strong of late with its ICDs, this is a market still ruled by Medtronic (NYSE:MDT) and Guidant (NYSE:GDT), with St. Jude holding roughly 14% market share. While Medtronic has had its problems of late, it's still a dominant force; its new Sentry device should be a major player in the ICD market. Guidant isn't quite as large as Medtronic, but it's a formidable competitor in its own right, and its approaching merger with Johnson & Johnson (NYSE:JNJ) certainly isn't going to hurt its long-term competitiveness.

Once nearly considered an also-ran that was destined to be bought out, St. Jude has remade itself into a growth stock. Trading at more than 30 times earnings and free cash flow, though, there is already a lot of optimism built into this stock. Investors looking for a way to play the stunning growth in ICDs may want to take a closer look at St. Jude, but to this Fool the combination of high valuation and strong competition is more than my heart can take.

Fool contributor Stephen Simpson holds a CFA. He owns shares of Johnson & Johnson.