Market conditions change relatively frequently. Equities seemed to be doing fine a year ago, but the picture doesn't look so good now. However, the basic playbook of the long-term investor remains the same regardless of these changing dynamics: hold on to shares of excellent companies through thick and thin -- and even as the market is experiencing a downturn.

Let's look at two healthcare stocks worth buying today and holding on to for a long while: Intuitive Surgical (ISRG 0.15%) and Abbott Laboratories (ABT 0.04%).

Intuitive Surgical

Medical devices giant Intuitive Surgical has some critical attributes that companies need to succeed in the long run. Thanks to its da Vinci Surgical System, it is the leader in its industry, the robotic-assisted surgery (RAS) market. The company's business also benefits from a strong competitive edge. The da Vinci system typically costs between $500,000 and $2.5 million.

That's not an insignificant sum for many healthcare facilities, and it is unlikely that many will change to one of Intuitive Surgical's competitors. In other words, the company benefits from high switching costs. Its products are also protected by hundreds of patents in the U.S. and abroad.

Next, the RAS market is arguably still in its infancy. Last year, medical devices specialist Medtronic estimated that only 3% of surgeries worldwide are performed robotically.

Intuitive Surgical's sales should continue growing as RAS surgeries make headway. The company makes the bulk of its revenue both by selling its da Vinci systems as well as through its instruments and accessories. Revenue from instruments and accessories is tied to the number of procedures performed. Analysts forecast that the company's revenue will grow at a 17.9% annualized rate over the next five years.

Intuitive Surgical did encounter serious headwinds during the pandemic. The volume of elective surgeries dropped amid the outbreak, which harmed the company's top line. But these pandemic-related obstacles are temporary. Competition may be a more permanent challenge for Intuitive Surgical. Medtronic and other healthcare giants, including Johnson & Johnson, have thrown their hats into the RAS industry.

Even so, it isn't rare to see multiple companies become highly successful in the same market. While competitors may eat up some of Intuitive Surgical's shares, in the long run there should be more than enough space for these companies to coexist. That's why Intuitive Surgical looks like an attractive healthcare stock buy for investors with a horizon of a decade or more. 

2. Abbott Laboratories

Abbott is another medical devices specialist, but its business is more diversified than Intuitive Surgical's. Abbott operates across three other divisions, including diagnostics, established pharmaceuticals, and nutrition. The diagnostics segment performed well amid the pandemic; Abbott manufactured and sold various successful coronavirus diagnostic tests, helping its revenue and earnings stay afloat while sales of medical devices took a hit.

Still, Abbott is best-known for its medical devices and boasts dozens of them, many of which also benefit from patent protection. Some of Abbott's most important products are within its structural heart, heart failure, and diabetes care units, and there are important reasons why. The incidence of chronic illnesses (including diabetes) is on the rise, and at the same time, the world's population is aging.

Older adults are more likely to suffer from various heart problems, and of course, a rise in the population of diabetes patients will increase the demand for innovative products of the sort Abbott Laboratories offers. The company's devices in these markets include its Amplatzer Amulet and MitraClip, both of which are devices to treat various serious heart-related conditions.

Meanwhile, Abbott's FreeStyle Libre is a leading continuous glucose device system that continues to make headway. Expect Abbott Laboratories' top line to be northbound thanks to these and many other products. Analysts see the company's revenue growing by a 12.6% annual rate over the coming five years, which would be a solid performance for a medical devices giant.

Abbott is also a Dividend King, having raised its payouts for 50 consecutive years. While the company's yield of 1.72% does not seem particularly generous -- it is barely higher than the S&P 500's 1.69% -- Abbott's dividend payout ratio of 39.7% is very conservative and leaves room for more increases. 

Between Abbott's dividend, diversified business, and growth opportunities, the company's shares look attractive for the long run.