That whiff of pot that drifts your way at a rock concert or outdoor event could damage your heart and blood vessels as much as secondhand cigarette smoke does, preliminary research suggests. Blood vessel function in laboratory rats dropped by 70 percent after a half-hour of exposure to secondhand marijuana smoke -- similar to results found with secondhand tobacco smoke, researchers from the University of California, San Francisco reported Sunday. Reduced blood vessel function can increase a person's risk of developing hardened arteries, which could lead to a heart attack. "Smoke is smoke. Both tobacco and marijuana smoke impair blood...