Two constant threads that have run through the history of North Korea: Rule by the Kim dynasty and speculation about the health of its secretive leaders.

The latest incident took place this week when U.S. officials said Monday they were unsure of Kim Jong Un’s health after they were told he was in critical condition after undergoing cardiovascular surgery. South Korea’s presidential office subsequently said Kim was conducting normal activities in a rural part of the country.

Heavy smoking, bulging waistlines and mysterious ailments have passed from state founder Kim Il Sung to his son Kim Jong Il and then to his grandson, fueling countless speculative reports about their treatments and prognoses. Their actual health condition has been known only by a small circle of their most-trusted aides, with the outside world in the dark.