The Brazilian's health had been disintegrating ever since a heart attack in November 2012.
"The little motor's in here," she says.
Three and a half months since a grueling but successful operation to replace her heart in the middle of the Rio Olympics, Balthazar, 66, is amazed and thankful to be alive.
But even as the huge scar running down her chest fades, the emotions of owing her own survival to a man she never met and who first had to die himself remain almost too much to handle.
Balthazar's health had been disintegrating ever since a heart attack in November 2012. By August of this year, she could hardly walk or talk.
"I was in despair," she told AFP in a rare interview at her small, neat apartment in Rio de Janeiro.
Then the Olympics came, bringing hundreds of thousands of tourists and the world's best athletes. Among them was Stefan Henze, a German canoing team coach who had won silver in the 2004 Athens Games.
After the 35-year-old was fatally injured in a car accident, Balthazar got the call.
Under Brazilian law hospitals cannot disclose the organ donor's identity, but the German's death was all over the news and Balthazar's family soon put two and two together.
Now this unlikely pair -- a Rio grandmother and a tragically killed Olympian -- are bound in the strangest, deepest possible intimacy.
"When I'm alone," Balthazar says, "I really put this hand on my heart and declare: 'My God, this boy brought me back to life.'"
Balthazar was a smoker and the hard-charging boss of her own human resources agency. Life was "work, work, work," she said.
Then came the heart attack and, despite attempts to treat her condition, a terrifying decline in which she could literally measure the slow motion breakdown of her heart, the pulse rate dropping down to 49 beats a minute. "It had almost stopped."
In January 2015 she entered the heart donor waiting list at number eight. An intensive series of exams followed to verify that she'd be healthy enough to go through an eventual operation.
In May this year she had moved to first place, but was locked in a race against death. "I already wasn't able to breathe properly," she said.
Twice a week -- Wednesdays and Fridays -- the hospital called on her cellphone to check her condition. "Then they called on a Monday... and said come."
Balthazar was terrified as she went into the operating theater that August 15. She told her son Fabio and daughter Renata that she was "prepared to die."
Today Balthazar still has trouble eating, suffers poor coordination and wears a surgical mask in the street to protect her weak immune system. But she is recovering rapidly.
"Everything has changed in my health. I couldn't do anything before," she says. "I wouldn't be here talking with you."
Next year she even plans to take part in a run with other transplant patients, dedicating the race as a "homage" to Henze.
The bigger change is in her attitude. She dreams of getting back to work, but also of enjoying simple things and watching her five grandchildren grow.
"I had such a busy life before," she says. Now "I say to people: Pause, think -- work is necessary but it's not healthy."
Although she sent a letter of thanks to Henze's family via the German consulate and would like to "give his mother a hug," she's "not emotionally ready" for more direct contact.
But she thinks a lot about the dead athlete.
"I looked for more information on him but didn't find much. I found out about his professional life but on his personal life I found nothing. I would like to know more about his life," she said of her savior. "I know he was happy, a lively person."
And she makes a vow: "To look after this heart very carefully."