The cause of death is stated to have been "accidental" (meaning there is no evidence of any intentional acts to put the victim into that situation of distress). The stress of that situation (which was created by accident) is believed to have triggered the arrhythmia (to be distinguished from a myocardial infarction (aka "heart attack").
To me it seems like the cause of death should be ‘natural causes’. Of course I don’t believe it regardless of what they say. The whole thing is to suspicious all things considered.