I'm sure a lot of you know this, but according to an article I just glanced at on the Internet so you know it's true, slightly more than half of people are actually not quite correct about where their heart is.
So, just for the record: your heart is in the middle of your chest, basically, not over on the upper left quadrant. It's not symmetrical, so a bit more of it IS to the left than to the right of the centerline, and the parts to the left are a little closer to the front than the parts on the right, which is why you might THINK it's on the left, but it's mostly in the middle. People tend to imagine it a lot farther over to the left than it really is.
So, just for the record: your heart is in the middle of your chest, basically, not over on the upper left quadrant. It's not symmetrical, so a bit more of it IS to the left than to the right of the centerline, and the parts to the left are a little closer to the front than the parts on the right, which is why you might THINK it's on the left, but it's mostly in the middle. People tend to imagine it a lot farther over to the left than it really is.