This is not a joke.
It came from the New England Journal of Medicine:

Great news for girl watchers:

Ogling over women's breasts is good for a man's health and can add years to his life, medical experts have discovered. According to the New England Journal of Medicine, "Just 10 minutes of staring at the charms of a well-endowed female is roughly equivalent to a 30-minute aerobics work-out," declared gerontologist Dr. Karen Weatherby. Dr. Weatherby and fellow researchers at three hospitals in Frankfurt, Germany, reached the startling conclusion after comparing the health of 200 male outpatients - half of whom were instructed to look at busty females daily, the other half told to refrain from doing so.

The study revealed that after five years, the chest-watchers had lower blood pressure, slower resting pulse rates and fewer instances of coronary artery disease. "Sexual excitement gets the heart pumping and improves blood circulation," explains Dr. Weatherby. "There is no question: Gazing at breasts makes men healthier." "Our study indicates that engaging in this activity a few minutes daily cuts the risk of stroke and heart attack in half. We believe that by doing so consistently, the average man can extend his life four to five years."