Boris Yeltsin has been hospitalized with an apparent heart attack for the second time in four months. Although dogged by persistent health problems, the 64-year-old Russian President had appeared fitter in recent weeks, enough so to challenge French President Jacques Chirac to a tennis match. "Considering that Yeltsin has already outlived the average Russian male by seven years, Yeltsin's condition can be considered serious," says TIME's Sally Donnelly in Moscow. "It is unknown how long he will remain in the hospital, although a week is the common period. However, the three presidents from the former Yugoslavia are due in town on Tuesday, so unless his condition is life-threatening, Yeltsin will probably show up."