The main finding was that when rats were exposed to secondhand smoke from marijuana for one minute, their arteries became less efficient at carrying enough blood for at least 90 minutes, whereas similar exposure to secondhand smoke from tobacco caused impairment that fully recovered within 30 minutes (exposure to clean air in the exposure chamber did not cause impairment). (It is important to understand that arteries of rats and humans are similar in how they respond to tobacco smoke, so the response of rat arteries to marijuana smoke is expected to be a valid indication of how human arteries respond to marijuana smoke.)