When Dr. David Kao tells patients they have atrial fibrillation—an irregular and often rapid heart rhythm that can lead to stroke, blood clots or other health issues—their first question is usually "Do I have to give up coffee?"

His answer often surprises them: No.

"They're thrilled," said Kao, a cardiologist and an associate professor at the University of Colorado School of Medicine in Aurora. For many people with heart disease, "coffee has been part of their daily routine forever, and they're already giving up so much. It just keeps people feeling normal in one way, when in a lot of ways, they don't feel normal anymore."

Blame their assumption on caffeine, which gets coffee lovers going in the morning and may keep them alert when the daily doldrums set in.

"Because it's a stimulant, they feel their heart is going to race and be worse off, especially when you have an arrhythmia like atrial fibrillation," said Dr. José Joglar, a professor at UT Southwestern Medical Center in Dallas and head of its arrhythmia program. "But it's not in the science."

Joglar was the lead author of new guidelines from the American College of Cardiology and the American Heart Association on diagnosing and treating atrial fibrillation, or AFib, published recently in Circulation. Among the detailed discussions of lifestyle habits, risk modification, treatments and the complexities of AFib, the authors included specific reassurances that caffeine isn't the problem.

Studies "have generally found that caffeine consumed in usual amounts is either associated with no heightened risk or a reduced risk of incident atrial fibrillation," the report said.

"The bad reputation that caffeine has is not deserved," Joglar said. "Caffeine has been shown to be safe for the heart."

Moreover, it may even do some good. A 2021 study published in the journal Circulation: Heart Failure suggested that caffeinated coffee may actually reduce the risk of heart failure. The research analyzed three studies and showed that "increased coffee consumption appeared to correlate with reduced risk of developing heart failure later in life."

Kao, the senior author of the analysis, invokes the research to reassure patients who develop heart problems and blame coffee.

"People think they may have been harming themselves the whole time," he said. "They've been a lifelong coffee drinker, and they think that's why they have atrial fibrillation, which does not seem to be the case. I think that's a relief that it's not their fault."

Up to 400 milligrams of caffeine a day—roughly four or five cups of coffee—can be safe for healthy adults, according to the Food and Drug Administration.

However, this cup of good cheer does come with a few caveats.

"There are always some patients who are more sensitive to caffeine," Joglar said. "Those patients should be careful. It can make you feel worse. Of course, you'll get jittery if you're drinking too much." But for the average person, he said, coffee likely is not detrimental to their health.

Kao agreed. "There may be other reasons people may want to stop drinking coffee, like sleep disorders or anxiety disorders," he said. "But not for the sake of the heart."

The coffee-friendly AFib recommendations don't extend to every heart condition or high blood pressure. To be sure, Joglar advised, talk to your doctor.

Nor do they extend to every kind of coffee. Kao said most studies focus on caffeinated black coffee—not decaffeinated coffee or instant coffee, where the processing may remove some of the health benefits. "I think the jury is still out on the decaf question," he said. "It would be really helpful to know."

The same holds true when it comes to another major source for caffeine in the U.S.: sodas, especially those with artificial sweeteners. "We just haven't broken it down enough," Kao said.

Although Joglar is a coffee lover—"I always thought caffeine is a superfood"—he's not referring to coffee-based beverages enhanced with sugar, flavored syrups, whipped cream and other caloric delights, which no studies say are good for the heart.