This Tiny Detail About Jack's Past On 'This Is Us' Has A Major Impact On This Future

Ron Batzdorff/NBC

On This Is Us, the episode "Vietnam" told viewers that the Pearson brothers' experience with war wasn't exactly the moving, Band of Brothers-esque journey that Jack's faded group photo suggested. Although the show has implied that Jack and Nicky are eventually stationed alongside each other, "Vietnam" revealed that because of his health, Jack wasn't even supposed to fight in the war. His death following the house fire might have been a shock to Rebecca, but it turns out that Jack's heart condition on This Is Us is more serious than fans thought.

While Michael Angarano's Nicky was conscripted in 1969 based on his birthday, big brother Jack was initially considered unfit to go to war. As the Pearson family doctor reminded him, he had an irregular heartbeat that Jack often covered up with the excuse of being nervous. But when Jack insisted that he had to go to Vietnam just to be near a struggling Nicky, the doctor gave him advice on how to pass his medical exam without being questioned. While the episode didn't offer any hints of Jack's heart giving him issues during the war, it did reveal that his heart was a problem even when he was a kid.

Ron Batzdorff/NBC

Not only did this medical insight add an extra level of risk to Jack's enlistment, but the knowledge makes the nature of Jack's death even more heartbreaking. Although he made it out of the Pearson house fire in 1998 alive, he inhaled too much smoke and later died of cardiac arrest at the hospital. Clearly, his heart condition wasn't exactly monitored later in life, perhaps because Jack's alcoholism began to dominate his health a little more than a decade after he came home from war. Milo Ventimiglia told Entertainment Weekly about the condition, "Again, different era. When Jack was growing up, mom and dad were smoking in the house."

Fans on Twitter quickly connected the detail with Jack's future timeline, definitely reliving the trauma of that emotional post-Super Bowl episode.

We don't know whether Jack ever told Rebecca about his heart condition, but if there's anything the Vietnam storyline has emphasized, it's that Jack remained tight-lipped about his life before his future wife was in the picture. Since Jack seemingly downplayed the truth about his heart his entire life, it wouldn't be totally surprising if Rebecca never knew. This pattern of little details in early timelines providing information for later years ought to continue, and we already saw how the origins of Jack's breathing method with Randall traced back to the war. At Nicky's birth, Jack's dad also reminded him that his only job was to be a big brother and look after Nicky, which parallels Jack telling Kevin and Randall the same thing when they fought as teens.

Ventimiglia has also had the strange experience of filming scenes that feel familiar of older Jack, despite the scenes' chronology fitting in before what the actor has already shot. He told EW:

There have been so many moments throughout shooting this Vietnam storyline that I realized every moment that is happening to Jack in Vietnam is a moment that we’ve already played later on in his life. In later episodes, when we’re doing more Vietnam stuff, things will happen, and I’m like, “Holy sh—. I remember when I was filming this one scene from his 50s or his 40s, and this totally informs that.” Eerily so, to where I feel like these things just soaked in through who Jack is and really, really formed him.

It looks like fans are in for a comprehensive and teary look at how Jack's time at war fully shaped the Jack Pearson that Rebecca and the Big Three are still mourning today. Season 3 of This Is Us continues on Tuesday, Oct. 23, at 9 p.m. ET on NBC.