The following report, titled "Sporadic Exercise, Even Sex, May Boost MI, Death Risk" does not come from the primary scientific literature, but from a medical newsletter to which I subscribe for professional reasons.
Here is the link: Sporadic Exercise, Even Sex, May Boost MI, Death Risk
One may read the article for free, but one may be required to sign up to do so.
Here's some of the text, if you don't want junk mail.