Health Care REIT ( HCN) agreed to buy Windrose Medical Properties ( WRS) in a deal worth about $451 million.

The transaction will also see Health Care REIT assume $426 million of Windrose debt. The merger will create a company with more than 550 properties in 37 states and gross real estate assets of roughly $4 billion.

Each share of Windrose will be exchanged for 0.4509 shares of Health Care REIT. At Tuesday's closing prices, Windrose is being valued at $18.06 a share.

Health Care REIT, Toledo, Ohio, invests in health care and senior housing properties. Windrose is a real estate investment trust based in Indianapolis.

Shares of Windrose gained $2.51, or 16.5%, to $17.69 in premarket trading Wednesday. Health Care REIT last closed at $40.05.