Energy drinks are causing potentially fatal heart disorders that are not explained by their high caffeine content, a study has found.

Experts have warned people with congenital heart conditions and high blood pressure to limit their use of the drinks after the largest study yet found they caused substantial interference in the electric signals that govern the organ.

A trial of participants between the ages of 18 and 40 revealed the speed at which the heart reset itself after beating was altered at least four hours after consuming an energy drink.

However, while the beverages tested were high in caffeine - between 304 and 320 milligrams per 32 fluid ounces - scientists would not expect to see electrocardiographic changes at doses under 400.

Instead, they believe the disturbance to the heart is being caused by an ingredient or combination of ingredients they do not yet understand.

Thirty-four healthy volunteers were given either an energy drink or a placebo on three separate days.

The research team at the University of the Pacific measured the electrical activity of the volunteers' hearts by electrocardiogram.

They also recorded participant's blood pressure.

All measurements were taken at the study's start and every 30 minutes for four hours after drink consumption.