WASHINGTON — John Medlin Jr., who presided over Wachovia Corp. during a 17-year period when its assets grew tenfold and it became a national banking institution, died Thursday. He was 78.

Mr. Medlin died of a heart attack while playing tennis at a country club at Grandfather Mountain, near Linville, N.C., according to Sheffield Hale, his son-in-law. He lived in Winston-Salem, N.C.

During his tenure as chief executive, from 1977 through 1993, Wachovia’s assets grew from $3.6 billion to $35.3 billion, the New York Times reported in 1993. Mr. Medlin joined Wachovia, based in Winston-Salem, in 1959, and he served as chairman until 1998.

“He was an old-fashioned banker who thought his responsibility was to the customers and keeping the bank safe and sound,” Paul Volcker, former chairman of the Federal Reserve, said Friday.

In a 1999 oral history interview, Mr. Medlin said, “Shareholders don’t really care about how big you are. They care about what happens to their stock. Customers don’t care about how big you are. They care about the service that you give them.”

Mr. Medlin was an early backer of First Union Corp.’s successful acquisition of Wachovia in 2001. Seven years later, the collapse of the subprime-mortgage market produced a $24 billion loss at Wachovia for the third quarter in 2008, leading to its sale to Wells Fargo & Co., announced in October of that year.

Wells Fargo, based in San Francisco, replaced the last Wachovia signs in its branches last year.

“But Wachovia will always be indelibly etched on my mind and in my heart,” Mr. Medlin told Business North Carolina in 2011. “It was my life for 40 years or so.”

John Grimes Medlin, Jr. was born in Benson, N.C.