Finding stocks that have true staying power for your portfolio isn't always easy. In today's historically overpriced market that could potentially be on the verge of another correction, it's more important than ever to focus on high-quality companies that can lend sustained growth to your holdings. Companies operating in non-cyclical industries -- sectors where demand is continuous regardless of market or economic conditions -- often prove to be the most resilient investments amid market ups and downs.

Healthcare is one such industry. The following two top healthcare stocks have a lot to offer the long-term investor, from solid histories of balance-sheet and share-price growth to robust dividends to compelling brands and durable competitive advantages.

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1. Pfizer

Pfizer (PFE 2.40%) was an established leader in the pharmaceutical industry with close to two centuries in business before the coronavirus pandemic brought the company to the public eye. But there's no disputing that the success of Comirnaty, the coronavirus vaccine it developed with BioNTech, has ushered in a new era of growth for the company. Comirnaty, which on Aug. 23 garnered the distinction of being the first coronavirus vaccine to receive full approval from the U.S. Food and Drug Administration, is on track to generate revenue of more than $33 billion for the company in 2021.

In the first six months of 2021, Pfizer reported that its revenues surged by an incredible 68% from the same period in 2020. Meanwhile, its net income during the same six-month window popped 53% year over year.

Previously, the company was known for more modest, albeit steady, rates of revenue growth. For example, in 2018, Pfizer reported 2% revenue growth, followed by a slight 1% decline in in 2019. And in 2020, management said revenue increased 3% from the prior year.

While Comirnaty has been a crucial factor behind Pfizer's recent quarterly performance, it isn't the only reason for these glowing top- and bottom-line figures. The company divested itself of its Upjohn division late last year in a spin-off with Mylan, forming the company now called Viatris. Upjohn was the company's generics division, and its lineup of poorly performing and older drugs was dragging down Pfizer's overall financial performance.

With Upjohn no longer in the picture, Pfizer's balance sheet is shaping up better than ever. Its stable of top-selling drugs, which treat everything from cancers to immune disorders to rare diseases, continues to generate high demand and rake in profits for the company. Case in point: In the second quarter of 2021, Pfizer's revenue, exclusive of Comirnaty, surged 10% year over year; with the coronavirus vaccine included, its top line jumped 86% year over year.

Another bright spot for investors is Pfizer's dividend, which yields 3.3% based on current share prices. Pfizer regularly increases this dividend, paying out $4.4 billion in dividends to shareholders during the first half of 2021 alone -- a 3% hike on a year-over-year basis.

Pfizer's consistent history of dividend increases, not to mention its steady price appreciation (the stock is up 30% year to date), make this healthcare stock a super-smart buy that can boost your portfolio's returns over the long term.

2. AbbVie

Pharmaceutical stock AbbVie (ABBV 1.06%) is another premium buy in the healthcare industry that can help investors snag consistent portfolio returns in the form of both share-price increases and quarterly dividends. Shares of the company are up about 15% year to date and have risen by close to 30% over the past year. However, it's AbbVie's dividend that really takes the cake.

AbbVie is one of a very short list of companies that have made it into the elite club of stocks known as Dividend Aristocrats. And the company's yield is more than three times that of the average stock that trades in the S&P 500, delivering 4.3% for shareholders at the time of this writing.  

AbbVie has long held the distinction of being the company with the world's top-selling pharmaceutical drug, Humira, which raked in sales of about $20 billion in 2020 alone. The drug treats conditions ranging from rheumatoid arthritis to Crohn's disease to moderate-to-severe plaque psoriasis. Although AbbVie will lose its U.S. patent exclusivity for Humira in a few years, the drug should still continue to provide a notable stream of revenue for the company.

AbbVie also has plenty of other golden eggs in its basket, such as Skyrizi (for moderate to severe plaque psoriasis), Rinvoq (for rheumatoid arthritis), and Imbruvica (for multiple types of blood cancer). Then there's the host of products that the company acquired when it bought Allergan last year. These include Botox Cosmetic for smoothing facial lines and Restasis, a chronic dry eye treatment.

In the second quarter of 2021, AbbVie reported that its total net revenue jumped 34% year over year. The company also delivered exceptional year-over-year results across its blood cancer, neuroscience, immunology, and aesthetic products portfolios with growth of 14%, 99%, 15%, and 100%, respectively.

AbbVie is a rock-solid pick for buy-and-hold investors seeking to add a dose of stability, consistent growth, and an exceedingly attractive dividend stock to their portfolio.