As the saying goes, nothing is certain except death and taxes. So long as the former continues to haunt humans, there will be a high demand for cutting-edge medical services. That makes the healthcare industry an excellent place to look for "forever stocks" -- but not just any company in the sector will do.

For those with $1,000 to spare that's not earmarked for routine expenses or emergencies, let's consider two healthcare stocks to invest in and hold onto for the long haul: Pfizer (PFE 2.20%) and Intuitive Surgical (ISRG -0.79%).

1. Pfizer

Pfizer hasn't been a popular stock in the past couple of years. Many investors still aren't sold on the company's prospects, given its declining coronavirus-related revenue and upcoming patent cliffs.

Indeed, Pfizer will lose patent exclusivity for some important products later this decade, including anticoagulant Eliquis, one of its best-selling medicines. However, Pfizer has significantly changed and improved its business in the past five years, thanks to a series of acquisitions and divestitures.

The new-look company has an incredibly deep pipeline across several areas and continues to earn approvals for brand-new products. It should be able to maintain that momentum in the foreseeable future. Pfizer boasts some promising candidates, such as its investigational weight loss drug danuglipron The company's success in developing a COVID-19 vaccine with BioNTech allowed it to double down in that area.

Pfizer's vaccine pipeline features more than a dozen programs, most of which are new entities. That includes some products targeting current areas where there are currently none. There's no approved vaccine for Lyme disease in the U.S., for instance, and Pfizer has a candidate in phase 3 studies. That barely scratches the surface of the company's pipeline.

Long-term investors should focus on the fact that Pfizer is a leading drug developer that has proven to be highly innovative and is led by an astute management team. The company's success in the coronavirus market wasn't just due to management's wise decision to partner with BioNTech -- which had done the groundwork to create their successful vaccine.

Pfizer also quickly developed Paxlovid, one of the most effective and successful medicines for COVID-19. Few things can allow a company to be successful over the long run like exemplary stewardship and innovative capabilities.

Lastly, Pfizer is a solid pick for dividend investors. Its current yield tops 5.75%, and management has consistently highlighted the company's focus on rewarding shareholders with dividends. Reinvesting the dividend will help boost long-term returns. With shares at just $29 apiece, investors can get 34 shares of Pfizer with change to spare.

2. Intuitive Surgical

Intuitive Surgical is on a roll. Earlier this year, the medical device specialist earned clearance for the fifth generation of its famous da Vinci system, a robotic-assisted surgery (RAS) device.

This new addition to Intuitive Surgical is already having a meaningful impact. In the third quarter, the company placed 379 da Vinci systems, 110 of which were the latest iteration of its crown jewel. Just six months after clearance, demand is already strong. Intuitive Surgical's revenue grew by 17% year over year to $2.04 billion.

Da Vinci procedure volume jumped 18%, compared to the year-ago period. Intuitive Surgical's financial results were excellent, but the company's prospects look even better. RAS devices like the da Vinci system facilitate minimally invasive surgeries performed by small incisions and with tiny, highly maneuverable instruments. This contrasts with open surgeries, which require somewhat significant skin incisions.

Minimally invasive procedures have many advantages, from less bleeding and scarring to faster recoveries, and Intuitive Surgical is the leader in the RAS market. The company's installed base as of the third quarter was 9,539, an increase of 15% year over year.

These machines are expensive -- costing about $1 million or more -- depending on the model. If they malfunction, it's easier to fix them (a service Intuitive Surgical offers) than to jump ship. In other words, Intuitive Surgical benefits from switching costs.

We can only expect the company's procedure volume to increase over the long run, given the world's aging population. Intuitive Surgical, a pioneer in RAS, looks likely to profit from the growth the industry will experience, considering its solid financial results and strong moat. The company's shares are changing hands for about $518 each, so investors can grab one with $1,000.