Your husband’s doctor’s advice is correct. The active components in fish oil is EPA and DHA and they both have been shown in recent research to be pro-arrhythmic and can cause AFIB and other arrhythmias, particularly at higher doses and in older people. Above 1 gram per day is generally considered high dose.

Fish oil also promotes bleeding and hemorrhagic stroke and is contraindicated in people taking anti-platelet, anticoagulant, aspirin, etc. medications. Fish oil could potentially cause your husbands leaky heart valve to leak even more from its blood thinning effects.

Similarly, other peer reviewed research shows the benefit of taking fish oil is no better than a placebo and can actually be dangerous in some people.

The one indication for taking fish oil is for people with high triglycerides that can’t be controlled by diet or other medications.