Institutional investors and hedge funds are selling stocks at an unprecedented pace, according to BNN Bloomberg. That's not too surprising, as it's clear we're in a bear market, which results from many investors selling many shares of stock, sending stock prices down sharply.

Still, not everyone is selling. Smart individual investors know that market downturns can present great buying opportunities, and hedge fund managers and other top investors know, too.

Here are five stocks that various big investors have been buying.

1. Medtronic

Ray Dalio heads Bridgewater Associates, one of the largest hedge fund companies around, if not the largest. The company's biggest new buy over the last quarter was shares of medical device specialist Medtronic (MDT -0.45%). Bridgewater spent more than $200 million on shares, making it the 18th-largest holding for the company.

Medtronic, with a recent market value topping $116 billion, has a lot going for it. The company describes itself like this on its website (with italics mine): "We innovate solutions that treat more than 70 health conditions, from Parkinson's to diabetes. And while our healthcare technologies transform the lives of two people every second, every hour, of every day, expect more from us."

Medtronic already has more than 49,000 patents in its portfolio, and spends more than $2.5 billion annually on research and development, pursuing new products and improvements to existing products. It has competitors, but few can spend that kind of money to further growth via innovation. One promising new offering is its Hugo robotic-assisted surgery system. The company even pays a dividend, recently yielding 3%.

2. Advanced Micro Devices

One of the richest hedge fund managers around is James Simons of Renaissance Technologies, with an estimated net worth recently topping $3.4 billion. One of Renaissance Technologies' new buys in its last quarter was Advanced Micro Devices (AMD -2.39%).

The chipmaker, often referred to as AMD, has many investors bullish about its acquisition of fellow chipmaker Xilinx earlier in the year, as demand for Xilinx's chips is expected to be robust. Hyperscale data centers, for example, often use Xilinx technology. Meanwhile, AMD has been growing its market share of the PC CPU market at the expense of industry leader Intel. In its last quarter, AMD's revenue was up a whopping 71% year over year.

3. CSX

Daniel Loeb of Third Point Capital may be feared by lots of companies, because he's known as an activist. When he takes a position in a company, there's a good chance he'd like to push for changes. In the last reported quarter, the biggest new addition to Third Point Capital's holdings was a quarter of a million dollars' worth of shares in railroad operator CSX (CSX 0.59%).

CSX's goal is "to become the best-run railroad in North America." Focused mainly on the eastern U.S., the CSX Transportation network includes about 20,000 route miles of track in 23 states, the District of Columbia, and the Canadian provinces of Ontario and Quebec. According to the company, nearly two-thirds of Americans live within its service territory.

The stock has been a solid performer (first-quarter revenue was up 21% year over year). While railroad transport is extremely economical, it's not perfect, as items transported still need to leave the tracks at some point and get to their final destination. So it's a promising move that CSX has acquired a trucking business that's already generating some 7% of revenue.

4. International Flavors & Fragrances

Carl Icahn is also an activist investor, and a more well-known one. In the last reported quarter for his holdings, the only new position was in International Flavors & Fragrances (IFF -0.65%), in which he invested $84.6 million dollars.

Tracing its roots back to 1889, the company may not be a household name, but it's a Fortune 500 company that supplies flavors, fragrances, and more to the food and beverage, fragrance, home and personal care, and health and wellness markets. Its first quarter featured revenue up 31% over year-ago levels, thanks in part to its merger with the nutrition and bio-sciences business of DuPont.

5. Chevron

Warren Buffett, considered by many to be the world's greatest investor, has grown the value of his company, Berkshire Hathaway, by an annual average of around 20% over 56 years. According its latest 13F filing, Berkshire increased its stake in oil giant Chevron (CVX -0.05%) by 316% in the last quarter, more than quadrupling it. Berkshire now owns a little more than 8% of Chevron.

In its first quarter, Chevron posted total revenue up a whopping 70% year over year. Many oil companies have been doing very well lately, especially in their "upstream," or extraction and production, activities. With Americans facing sky-high fuel prices, some wonder whether the government will step in and rein in profitability. Still, Chevron and other big oil companies have been investing in renewable energy and are multifaceted in their operations, making their long-term survival likely.

These are just a few companies that big-time investors have been buying recently. Since many stocks have tumbled sharply in recent months, some of the ones above may be trading at even lower levels than when these investors bought them. If any interest you, dig deeper into them to make sure they're a good fit for your portfolio.