As the leaders of China and Russia walked to the viewing platform at a military parade in Beijing on Wednesday, they made small talk about living forever.

Xi Jinping, China’s leader, mused that people might soon live to 150. President Vladimir V. Putin of Russia, speaking through a translator, said that organ transplants could allow humans to achieve “immortality.”

The fragments of banter were captured by a microphone and broadcast live by Chinese state news media from the parade celebrating the 80th anniversary of the end of World War II. It was a hot mic moment that shed light on how medical advances are intersecting with geopolitics, given that both Mr. Putin and Mr. Xi, who are both 72, have suggested they may want to stay in power for years to come.

Asked about the comments in a news conference later on Wednesday, Mr. Putin confirmed that the conversation had taken place.

“Modern health methods,” Mr. Putin told a reporter, “allow humanity to hope” that “life expectancy will grow significantly.” Among those advances, he said, were “medical means, even surgical ones, related to organ transplants.”

Mr. Putin has long been reported to take a personal interest in longevity, and he has tasked his health ministry with increasing life expectancy as a “key priority.” The nuclear energy conglomerate Rosatom, one of Russia’s most important state companies, said last year that it was developing technology to “print” human organs.