Stressful and emotional movies minor cause changes in heartbeat and a significant increase in blood pressure, according to a University College London study.

Researchers observed small changes in the heartbeat of normal and healthy individuals. The consequences can be destabilising and risky in patients with a weak heart, if they undergo extreme stress.

"This is the first time that the effects have been directly measured and although the results varied from person to person we consistently saw changes in the cardiac muscle," said Dr Ben Hanson of mechanical engineering department, in a statement.

The researchers conducted studies to determine the direct impact of mental and emotional stress on the human heart.

For the study, 19 patients associated with cardiac catheterization treatment were shown excerpts of the Hollywood film "Vertical Limits."

"Film clips are considered to be among the most powerful stimuli to elicit affective responses in the laboratory setting and have several advantages including their dynamic nature, a sustained effect and the combination of visual and auditory inputs," said study author Professor Peter Taggart (UCLH Neurocardiology Unit).

While the participants watched the clippings, researchers measured the changes in cardiac muscles by placing electrodes at the ventricles of the heart. Simultaneously, they also observed changes to blood pressure and breathing speed.

"Placing the electrodes in veins and positioning them on the inside of the heart can be quite stressful for the patient. Making sure the patients remained relaxed throughout the procedure was vital so that the electrodes only recorded emotional stress from the film clip," said Professor Jas Gill (Guy's and St. Thomas' Hospital Department of Cardiology), who conducted the clinical side of the study.

Researchers found that there were minute changes in the heartbeat and enhanced blood pressure levels in participants watching the movie.

In the second experiment, researchers asked the participants to mimic the breathing pattern they experienced while watching the clips. Here, the researchers did not find any irregular changes in heartbeat and blood pressure.

The finding is published in the journal Circulation, Arrhythmia and Electrophysiology.