What is a mini stroke? does it mean that something is wrong with the heart?

Possibly: Mini-strokes are colloquially thought of as transient ischemic attacks, or tias, which are neurologic deficits that may resolve over a relatively short period of time. Although these are commonly associated with disease of the blood vessels feeding parts of the brain, some may be a result of clots forming in the heart, e.g., sluggish contraction with blood sludging or atrial fibrillation.