TORONTO -- The Toronto Zoo says a second endangered tiger cub has died at the facility, leaving just one alive from the litter born less than a month ago.

The Zoo issued a Facebook post saying the Amur tiger cub named Small, who was born on April 30, was euthanized on Friday.

It says Small had been monitored closely since birth, as she was not gaining weight.

The zoo's medical team eventually discovered several heart defects, including a hole between the main chambers and a key blood vessel coming from the wrong side of the organ, which were too complex to be repaired.

Her death comes 10 days after another cub from the same litter was euthanized due to multiple ailments including severe liver damage.

Toronto Zoo Amur tiger cub

The zoo says the remaining cub continues to thrive and is monitored by zoo staff.

The cubs were born after their mother, an Amur tiger nicknamed Mazy, was paired with the male tiger Vasili through a program meant to promote conservation.