Boston Scientific: +26.34%

In the past couple of years, Boston Scientific has made good on CEO Michael Mahoney's promise to turn around years of sluggish performance. The company's stock has roughly tripled in value since late 2011, and grew steadily in 2015 thus far. In fact, a report from Evaluate Medtech found that the company's share price rose 34% in the first six months of the year--the biggest increase of any medtech company with $15 billion or more in revenue

In 2015, Boston Scientific's interventional cardiology business has been helping drive the company forward. The FDA approval of the company's Watchman left atrial appendage closure device (pictured) is a unique stroke treatment device that prevents clots from the heart from reaching the brain. It took years for the product to win FDA approval.

Last month, Boston Sci gained access to the billion-dollar market for cardiac monitoring products through a 27% stake in wireless heart-monitoring device maker Preventice Solutions (Houston, TX). The Marlborough, MA-based medtech giant is now the exclusive worldwide sales and marketing representative for Preventice's cardiology diagnostic and monitoring products.

Another promising Boston Scientific product is its Lotus TAVR device. Earlier in the year, the company predicted the device would bring in as much as $200 million by 2016.