The Indianapolis drugmaker says both a company doctor and Lechleiter's personal physician have cleared the 59-year-old to return.
Lechleiter had the surgery May 13. Chief Financial Officer Derica Rice served as acting CEO, and independent director Ellen Marram served as acting chairwoman.
Lechleiter was expected to make a full recovery from the surgery. The aorta is the largest blood vessel in the body, and Lechleiter's condition was discovered during unrelated testing. The executive had not experienced any symptoms.
Eli Lilly and Co. makes the antidepressant Cymbalta as well as several treatments for diabetes and forms of cancer.
Shares of Eli Lilly rose 29 cents to $50.87 in premarket trading Monday.