By Dan Diamond
The big are getting bigger: Aetna AET +1.74% and Humana HUM +0.62%, the nation’s number three and number four health insurers by revenue, are merging.
Aetna will pay about $230 per share for Humana, in a $37 billion cash and stock deal, the largest-ever deal in the health insurance industry. 
It’s also the latest major merger in an increasingly frantic health care marketplace. On Thursday, Centene CNC +1.23% announced that it was buying HealthNet for nearly $7 billion, and CVS last week bought the Target TGT +0.01% pharmacy business for $2 billion.
Aetna and Humana still need federal approval. But the combined company could become the nation’s number two health insurer, behind UnitedHealth Group … which had recently approached Aetna with its own offer to merge.
As health reporter Christopher Weaver cleverly framed it a few weeks ago,health insurers are playing a “Game of Thrones.”
But what crown are they after? And why are they merging now?