Kenley Jansen knew immediately what was happening. His heart was racing. His chest was tight. Each breath was a gasp.The same thing had happened in 2011 and 2012, each time when he was in the high altitude of Colorado. His heart was in atrial fibrillation.Most people would be terrified. Jansen was mad."I wasn't scared. I knew exactly what it was," he says now. "I was pissed."I thought my season was over. I'm like, man, f--- this. Not again. We're trying to go back to the World Series. I have a chance to win another Trevor Hoffman award. Man!"Jansen, now back on the active roster after being away from the team due to the irregular heartbeat on Aug. 9 in Denver, announced Wednesday that he would not travel with the Dodgers to Colorado this weekend, following doctor's orders."I tried everything to get it back into rhythm for 15, 20 minutes. And then I'm finally like, all right, let's just call 911."I remember being annoyed in the ambulance too. It was driving so slow. I just wanted to get to the ER so they could fix it."In this case, fixing it meant shocking his heart back into a normal rhythm, blood thinners to prevent clots, rest, heart medication to try to keep his heart in a normal rhythm and potentially another cardiac ablation surgery to correct the electrical issue that caused the problem in the first place."The doctors put a patch on my right side of my chest and on my left side of my rib cage. Then they just press a button, and it just hits. Oh man! It's a shock."It's really strong. But you feel better immediately because your heart's not racing and you can breathe again. But the next day you feel pretty bad. And the day after that, you feel terrible because of what your body has been through. It's a real trauma."Jansen was initially told he'd be out four to six weeks as his body recovered and adjusted to blood thinners. But after consulting with his doctors, he learned there was a chance for him to return faster. He could safely control the condition with medication until the offseason, when he'd have a second ablation surgery to correct the underlying electrical issue.When he returned 11 days later, though, something was off. The heart medication he had been taking left him feeling tired and unemotional. He gave up four home runs in his first two outings back, blowing two saves for a team that was fighting for a playoff berth."It was crazy," he says. "Normally if I give up a home run, I'm really pissed. I gave up four, and I felt nothing. It was like I had no emotion."I can't perform like that. I could do a 9-to-5 job. But not be an athlete, not be a closer."He told his doctors they had to adjust his medication. Jansen saved a league-leading 41 games last year. He has made the past three All-Star games. And the Dodgers' relief-pitching woes this season, with and without Jansen on the field, have been well-documented. In other words, the Dodgers desperately need him as both a closer and a leader.So does his family. His third child was born Aug. 14, and Jansen has been trying to reconcile his responsibility to his family and his team."To tell you the truth, I wanted to have the second surgery right now so we could just fix it and I'd know everything was OK," Jansen says. "But I know what an opportunity our team has this year and my responsibilities here."If we make the playoffs, I really think we can go right back to the World Series. But we have to make the playoffs, and every day is a grind."After his troubles on the mound while on his medication, he and his doctors decided to switch to aspirin. Every day he'd use an application on his iPhone to monitor his heart and send reports to his doctors. If anything was amiss, it would be caught quickly. The only way Jansen feels able to reconcile his responsibility to his team and his family is to trust his doctors, whether they tell him it's safe to wait on surgery until the offseason or unsafe to return for this weekend's critical series in Colorado."Whatever the doctor says, I respect that. You have to respect it. You don't try to be a hero," he says. "They took care of me six years ago, and I trust them."Though he made headlines last month for dramatic quotes about his decisions to play -- "I'm not thinking about my heart. ... If it goes, it goes," he said -- Jansen clarified that he just doesn't want to be afraid."You can't be scared of life. If something happens, what can you do? You don't know when God's gonna take you. I hope not for like 60-70 years. I hope to live here until I'm 100 and to watch all my kids grow up."When you live your life scared, that's when bad stuff's gonna happen."Jansen said that while doctors told him its not safe to travel back to Colorado this weekend, there's a chance he would be cleared to pitch there if the Dodgers face the Rockies in the playoffs.He's going to have an MRI this week, and the 3-D images doctors take of his heart will help them understand exactly what and where the underlying issue is. It's possible a different dosage of the heart medication he was on could allow him to pitch safely again, without as many side effects.It's also possible Jansen sits out any games the Dodgers play in Colorado until he can have the second ablation surgery in the offseason."I talk to my doctor all the time," he said. "He told me to call any time of the day or night. He's ready. He told me to just focus on the positive, on all the things that have gone right with this, and not the fact I have to go through it again or worrying about what could happen. Just stay positive."