The companies announced the takeover almost a year ago in December 2017, promising to create an integrated health-care company whose pharmacy locations could be hubs for medical services while better managing patients.

The goals of the deal — better-managed care, new points of access to the medical system, healthier communities — are extremely ambitious. Now the companies have to prove that they can actually achieve them in what’s likely to be an extremely complex merger. CVS said it will quickly start rolling out of products to do that: managing patients with chronic diseases, more services at in-store clinics, screenings, and offerings like nutrition counseling and digital health apps. If it works, the deal is likely to have long-term effects around the rest of health care, forcing investors and executives to ask whether companies that offer administrative services, distribution or act as middlemen should be independent.

Aetna shareholders will get $145 in cash and 0.8378 shares of CVS stock in the deal, making it worth about $212 a share. Including debt, the transaction is valued at about $78 billion, CVS said.