Cypress-based PacifiCare Health Systems Inc. said Wednesday it has agreed to acquired by rival UnitedHealth Group Inc. for a total consideration of $2.2 billion in cash and 111.6 million shares.

PacifiCare shareholders will receive $21.50 in cash and 1.10 UnitedHealth shares for each share held.

PacifiCare’s stock market capitalization at Tuesday’s closing price was $6.3 billion.

Upon completion, PacifiCare will operate as a wholly owned subsidiary of UnitedHealthcare. The deal remains subject to approval by PacifiCare shareholders and regulators as well as other customary closing conditions.

PacifiCare saw its shares surge as much as 13.2 percent in midday trading Wednesday after word broke that United was closing in on a deal to buy the operator of managed healthcare plans. Trading in PacifiCare, and Minnetonka, Minn.-based United, also a managed healthcare service plan operator, was halted on the news. PacifiCare eventually settled at $77.09, up 6.1 percent.

PacifiCare has seen a turnaround in the past four years under Chief Executive Howard Phanstiel, who introduced various plans and moved the company away from its old, narrow HMO image.

PacifiCare and other health plan operators also got a boost from a Medicare reform law passed in late 2003, which gave it and its rivals billions to introduce new products and lure seniors from traditional Medicare into managed care models. PacifiCare is one of the biggest players in the sector.

The deal is the latest in a round of consolidation by health insurers who have been combining to get leverage with hospitals and drug companies.

Last year’s $16.5 billion merger of WellPoint Health Networks Inc. and Anthem Inc. created the largest U.S. health plan with more than 28.5 million members. It is now called WellPoint Inc.

*Vita Reed of the Orange County Business Journal contributed to this article.