Kim Aris told Reuters that his 80-year-old mother, in military custody since a 2021 coup that deposed her government, had asked to see a cardiologist about a month ago, but he had been unable to determine whether her request had been granted.
"Without proper medical examinations ... it is impossible to know what state her heart is in," he said by phone from London on Friday.
"I am extremely worried. There is no way of verifying if she is even alive."
The Nobel Peace Prize laureate has also suffered from bone and gum issues, Aris said, adding it was likely she had been injured in an earthquake in March that killed more than 3700 people.
In a Facebook video, he appealed for Suu Kyi and all political prisoners in Myanmar to be released.
A spokesman for Myanmar's military-backed interim government did not pick up calls from Reuters seeking comment, and its information ministry did not immediately respond to questions sent via email.
Myanmar has been gripped by violence since the military takeover in February 2021, which prompted mass rallies that were crushed by brutal force, sparking a widespread armed uprising.
Suu Kyi, a long-standing symbol of Myanmar's pro-democracy movement, is serving a 27-year sentence for offences including incitement, corruption and election fraud, all of which she denies.
One of her last public appearances was in court in May 2021, a few months after the coup, when pictures aired by state television showed her sitting upright in the dock, with her hands in her lap and wearing a surgical mask.
The military justified its takeover on the basis of what it said was widespread fraud in an election that Suu Kyi's party won by a landslide, although election monitors found no evidence of cheating.
Foreign governments and rights groups have consistently called for her release.
Starting in late December, the military-backed interim government plans to hold new elections in multiple phases, the first polls since the one that triggered the coup.
