E-cigarettes and marijuana may have harmful effects on the heart similar to those caused by tobacco cigarettes, opening the door to abnormal heart rhythms, according to a study conducted in mice.

E-cigarettes and heated tobacco products have become popular because the public perceives them as being less harmful than smoking, the researchers said.

Similarly, legal recreational marijuana has become more common in recent years, and is also frequently viewed by the public as being safer than smoking tobacco, they said.

"We found that cigarettes, e-cigarettes, and marijuana greatly interfere with the electrical activity, structure, and neural regulation of the heart," said study lead author Huiliang Qiu, a postdoctoral scholar at the University of California, San Francisco (UCSF) in the US.

"Often, any single change can lead to arrhythmia disease. Unfortunately, these adverse effects on the heart are quite comprehensive," Qiu said.

The study, published in the journal Heart Rhythm, exposed rats for eight weeks to a single daily session of exposure to smoke, aerosol from a popular e-cigarette, aerosol from the heated tobacco product, smoke from marijuana, and smoke from modified marijuana that lacks all cannabinoids, compared to just air.

The exposures modelled a single session of actual smoking/vaping: The rats inhaled the smoke or aerosol for five seconds twice for five minutes, with clean air in between the smoke inhalations.

This was done once per day for five days and per week for eight weeks. During that time, the heart function in the rats exposed to the products (but not air) got progressively worse and blood pressure increased, the researchers said.

At the end of the study, the team conducted various tests to determine electrical and physical properties of the hearts.

The researchers found that all the products led to increased scarring in the hearts, a decrease in the number of blood vessels, a change in the type of nerves found in the heart, a reduction in the important ability to vary heart rate, and a higher likelihood of developing arrhythmias.

"It's notable that all of these tobacco and marijuana products had such similar effects," said senior author Matthew Springer, a UCSF professor of cardiology.

"And what's really striking is that this was caused by a single realistic smoking/vaping session per day," Springer said.

The researchers acknowledged that there are some limitations to the study.

"While rats are a good model for many cardiovascular effects of humans, there are still differences and one can't draw firm conclusions about effects on humans from rat studies alone," Springer said.

However, he noted that the results are consistent with various reports from the medical literature about heart rhythm disturbances in users of e-cigarettes or marijuana.

The observation of various physical disturbances in the heart, like the scarring and the nerve changes, suggests a similar explanation, despite the differences in nicotine or cannabinoid content, the researchers added.