I'm a little sore on the right-middle side of my chest from exercising yesterday, I'm thinking I just pulled a muscle.

No big deal, but I got to thinking that the hearts a muscle too. Is it possible to exercise to the point where your heart becomes sore like any other muscle can?
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i believe a muscle gets sore if you use it directly. (ie biceps after curls, chest after bench press)

if it weren't directly...you wouldn't be able to get your heart rate up that high to hurt it unless you were on some drugs or something