President Raul Castro's right hand man, Casas Regueiro was the number four person in the Cuban hierarchy when he dropped dead of a heart attack on Saturday at the age of 75. Above him on the power pyramid is the president, who celebrated his 80th birthday in June; first vice president Jose Ramon Machado, who will be 81 in October; and the historic revolutionary commander Ramiro Valdes, who turned 79 in April. "This death is a warning to Raul that there is little time left to retire the generation of historic leaders. It's a call to think seriously about replacements and the rejuvenation of the top leadership of the Communist Party," said Cuban analyst Arturo Lopez-Levy of the University of Denver. A loyalist among loyalists, Casas Regueiro was only the second defense minister since the Cuban revolution in 1959. In 2008, he succeeded Raul Castro, who for nearly half a century served as defense minister under his brother Fidel, 85, before officially succeeding the ailing Castro as president in February 2008. Next in line to succeed Casas Regueiro' is the armed forces' first deputy minister, General Leopoldo Cinta Frias, 70, who is expected to be officially nominated to the post after three days of mourning for his predecessor. Besides his military activities, General Casas Regueiro played a key role in promoting a major reform of the Cuban economic system, which was modeled on the Soviet system in the 1970s and severely crippled by the collapse of the Soviet bloc in the 1990s. As guardian of the military's finances, he helped make the military a major player in the Cuban economy under the aegis of the Group of Enterprise Administration (GAESA), whose flagship Gaviota holding company has invested in multiple areas, notably tourism. "He contributed to creating rational economic management by the military, in contrast with the civilian sector," said Oscar Espinosa Chepe, a dissident Cuban economist. At the end of a Communist Party congress in April that approved sweeping economic reforms, the average age of the members of the party's decision-making Politburo was lowered from 70 to 67. But that was achieved mainly by reducing its size from 19 to 15, as only three of its members are under the age of 65. "The other historic leaders of the revolution have little time left. The death of the armed forces chief underscores the absurdity of trying to cling to the past and resist reforms," Michael Shifter, president of Washington-based Inter-American Dialogue, told AFP. During the party congress, Raul Castor admitted that it was "truly shameful" that Cuba has not put in place "a reserve of replacements," with the experience and maturity needed to lead the party and the government. He then announced that people holding key offices would be limited to two terms of five years each. And he convened a party conference for January 2012 charged with finding ways of renewing the party rank and file.