Fish oil is rich in Omega 3 fatty acids, and is an excellent supplement for most heart patients. Flaxseed oil has Omega 3, 6, and 9 fatty acids.
It should be noted that Fish Oil is one of the very few supplements that has actually been shown to be effective for heart issues. It builds up in the system and reduces arrhythmias and helps to regulate the heart. There are dozens of positive studies on the cardiology journal sites, in PubMed and elsewhere. While some vegetable oils, like flaxseed, have a similar effect, it is not as fast or strong and doesn't last as well.
And it's pretty cheap.
It is best to look for fish oil (often salmon oil) that comes from wild sources, rather than farmed fish. Seaborne toxins, such as mercury, are higher in farmed fish than wild ones, and the oil is where these things tend to be concentrated.
If you take warfarin, you should be aware that it is known to have an anticoagulant effect. It may not register in your INR, though, as it may not operate through the same action, so be cautious. Also, everyone has different tolerances, so it may be a problem for one individual, and not bother another at all. If you are already having bleeding problems or are prone to them, it might not be a good choice for you.
Best wishes,