Co-lead author Matthew Tattersall, an assistant professor of medicine at the university, added: 'Immediately after vaping or smoking, there were worrisome changes in blood pressure, heart rate, heart rate variability and blood vessel tone (constriction).'
The results of both studies were presented at the American Heart Association Scientific Sessions 2022.
It comes amid a vape epidemic in the US, with around 8million adults and 2.5m minors using the devices. More than 3m Brits are regular users.
While e-cigarettes are often marketed as healthy alternatives to typical cigarettes - they contain many harmful chemicals of their own.
E-liquids contain nitrosamines, which have been linked to cancer, while flavored vapes often include diacetyl, an irritant linked to the deadly condition 'popcorn lung'.
Science is also beginning to show the devices can have as much a negative affect on heart health as smoking does.
In the latest study, researchers looked at data for 395 participants - 164 vapers, 117 smokers and 114 who had no history of nicotine, e-cigarette or tobacco use.
Researchers assessed blood pressure, heart rate, the diameter of the brachial artery in the arm and heart rate variability before vaping and smoking as well as 15 minutes afterwards.
Data show that people who vaped and those who smoked cigarettes had a pulse four beats per minute faster after a vape or smoke, whereas there was no change for the non-users.
The study also found that smokers and vapers had their blood pressure rise while using devices from 122/72millimeters of mercury (mm HG) to 127/77 mm Hg.
A second study, found vapers had worse exercise performance than non-smokers and that it was akin to that of smokers.
A first study found that people who vaped and smoked had an average heartbeat that was 4 beats per minute faster than those that avoided nicotine.
Dr Tattersall added: 'These findings suggest worse cardiovascular disease risk factors right after vaping or smoking, and activation of the sympathetic nervous system may play a role in the adverse responses seen immediately after using e-cigarettes and after exercise testing 90 minutes later.'
In a second study, the same participants were subject to a treadmill stress test.
After 90 minutes on the machine, they were given four heart screenings to determine overall health of the organ.
People who vaped scored 11 per cent lower than those who did not use nicotine.
Smokers had test scores 16 per cent lower than the control group.
They also had a larger difference from their reserve and maximum heart rate when exercising, signaling their hearts were working more during exercise.
The difference between reserve and exercising heart rate was 30 per cent higher among vapers and 40 per cent higher for smokers.
Smokers and vapers both achieved a lower cardiac workload that their peers who did not use nicotine and it took longer for their heartrate to return to normal after exercise.
While these findings are alarming, researchers warn that there is much more evidence about the downsides of using vapes.
Dr Aruni Bhatnagar, a professor of Medicine at the University of Louisville said: 'These studies add to the growing body of science that shows similar cardiovascular injury among people who use e-cigarettes and those who smoke combustible cigarettes.
'Additionally, it shows this cardiovascular risk is seen even among younger people who have a shorter history of nicotine use.'
'People should know that e-cigarettes and combustible cigarettes contain addictive nicotine and toxic chemicals that may have adverse effects on their cardiovascular system and their overall health.'
Dr Bhatnagar was involved in research published last week that found exposure to e-cigarette smoke caused drastic reductions in the heart rates of mice.
Another study funded by the National Institutes of Health last week found the blood vessels of mice constricted when exposed to e-cigarette smoke.
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