Healthcare giants Aetna (AET -Analyst Report) and Humana Inc. (HUM- Analyst Report) announced earlier they have entered into a definitive agreement under which Aetna will acquire all outstanding shares of Humana for a combination of cash and stock valued at $37 billion or approximately $230 per Humana share based on the closing price of Aetna common shares on July 2, 2015.

The merger has been unanimously approved by the board of directors of each company. Under the terms agreed upon, Humana stockholders will receive $125.00 in cash and 0.8375 Aetna common shares for each Humana share. As a result of the transaction, Aetna’s shareholders would own approximately 74% of the combined company and Humana’s shareholders would own approximately 26%.

Aetna and Humana have also agreed on a breakup fee of 3.75% of the deal’s enterprise value, currently about $1.4 billion, payable to either company if the agreement were to be broken-off for a higher offer from another party.

The combined company would have projected 2015 operating revenue of approximately $115 billion, with approximately 56% from government sponsored programs, which include Medicare and Medicaid. The combined company will have over 33 million medical members, based on memberships as of March 31, 2015.

Potential investors are currently cautious about this merger. Despite all the figures of the deal, any acquisition or merger of this magnitude, that is 2 of the 5 largest United States health insurance companies looking to become larger, must overcome 2 potential, yet critical, impediments.

Though the Aetna and Humana board of directors agreed to this deal in principle, the companies’ shareholders and the federal government must sign off on the merger as well. Aetna shareholders have much to discuss, since this deal is being funded with a large amount of the company’s stocks.

Another reason investors are skeptical is that Aetna is itself a potential target for a takeover. Last month, the Wall Street Journal reported that UnitedHealth Group Inc. (UNH) has approached Aetna about a deal to merge. If UnitedHealth makes another run at Aetna and comes away with a signed deal, Humana is walking away $1.4 billion richer.

There is too much uncertainty amongst the primary US healthcare juggernauts, especially with a potential merger between Anthem Inc. (ANTM - Analyst Report) and Cigna Corp. (CI - Analyst Report), for investors to make a well-informed purchase into any of these companies. Nothing drastic occurred today regarding the stock prices for both companies. Once an official decision is made on the merger, then investors can expect some more movement in this in-focus sector.