Investing.com - Two US healthcare giants will be joining forces. On Sunday, CVS, the largest drugstore chain, agreed to buy Aetna (NYSE:AET), the third-largest health-insurer, for around $69 billion. The deal will be this year’s largest corporate acquisition.CVS President and CEO Larry Merlo said the merger was, “to position the combined company as America’s front door to quality health care…to create a platform that iseasier to use and less expensive for consumers.” The announcement comes at a time when consumers are struggling under the weight of rising healthcare costs, and companies up and down the drug supply chain worry about the looming threat of Amazon (NASDAQ:AMZN) entering the pharmacy market.Antitrust approval has become an interesting question under the Trump administration, and the deal is subject to both shareholder and regulatory authorization. However, the transaction is expected to close in the second half of 2018.In a joint press release, CVS and Aetna said that shareholders are expected to benefit from a number of outcomes including the longer term potential to deliver significant incremental value. Following the announcement, CVS shares were down 1.8% to 73.5 dollars, while Aetna shares were 2% higher to $185.