Eli Lilly (NYSE:LLY) Chairman, President, and Chief Executive Officer John C. Lechleiter is taking a leave of absence from the company and will be temporarily replaced by Lilly Chief Financial Officer Derica W. Rice.

The company explained Monday that Lechleiter must step aside because of scheduled surgery to repair a dilated aorta. That surgery will be performed next Monday. According to Lilly, Lechleiter's departure will only be temporary, and he "is expected to make a full recovery and return to his duties later this summer."

Until that return, Rice will take the reins as interim CEO as dictated by the company's bylaws. Also, Ellen R. Marram, lead independent director on the board, will serve as acting chairman of the board.

Rice, a 22-year veteran of the firm, has served as CFO (traditionally the No. 2 spot in a company) for Lilly since 2006. Marram has served on the company's board for more than a decade.

Regardless, investors seem a bit shaken by the news. Lilly shares shed 1% of their value in Monday trading after the news came out, closing the day at $54.47.