[ by Melanie Gretchen ] Goldman Sachs' Edward Eisler and David Heller, co-heads of global securities division and long-time partners have announced their retirement.  Mr. Eisler and Mr. Heller as well as Pablo Salame and Harvey Schwartz ran the global securities division.  With their departure, London-based Isabelle Ealet has been named co-head with Mr. Salame and Mr. Schwartz. The move turned heads on Wall Street on Wednesday afternoon as it is unusual for two co-heads to retire on the same day.  Mr. Eisler and Mr. Heller are also the latest in a string of high level departures from the bank in recent months.  The firm, whose earnings have suffered over the past year in the wake of economic troubles abroad and continued malaise at home, has been shrinking.  It has laid off more than 1,000 employees worldwide and has been working to cut both its non-compensation and compensation expenses. [Dealbook, 1/11/12]