Why could gas cause heart palpitations?

The vagus nerve?: The association between GI activity (e.g. Gas/bloating, acid reflux) and palpitations exists, but we aren't sure why. It may involve the vagus nerve, which controls GI tract as well as the heart, especially the electrical properties of cardiac tissue. Alterations in vagus activity, triggered by GI feedback, may alter conduction properties in heart muscle, leading to fast or irregular heart beats.

Doesn't: Any association you've observed is purely coincidental.

Palpitations: In general gas wouldn't cause palpitations. In unusual circumstance a large gas bubble in the cardia of the stomach or in a hiatal hernia could stimulate the adjacent heart and cause palpitations. In the spectrum of palpitations, this would not be a frequent occurence however.