What causes heart palpitations?

Many things: Stimulants such as caffiene, energy drinks, decongestants such as psuedophedrine. Thyroid disease , anxiety, hormone imbalance are just a few causes.

Palpitations: These are caused by many things. Stress, excitement, irritants both physical and chemical, pressure like a hiatal hernia or esophageal push or pull, and primary heart things, the causes are very many in number.

Heart rhythm: Irregularities of the heart rhythm cause palpitations. Everyone has them sometimes. If you're bothered by them, seek further evaluation.