That is important to know. I am not sure if a pre-existing cardiac condition contributed to that. I do know fish oil was helpful for me as a supplement for moodswings (bipolar, not depression) but only as an adjunct to standard medications. It was initiated and supervised by my psychiatrist and I used that for an extended period of time. I do know that the anti-cholesterol medication Lovaza (which was developed from fish oil) is in clinical study as a mood stabilizer but of course it will take some time to see what the results are and if it is helpful if it can be used as more than an adjunct mood stabilizer.