How much cardio is too much?

Hey. Im 19 years old, male, 6 feet tall, about 165 lbs and around 15% body fat. I smoke a pack or more a day and havent started doing cardio til recently. Im trying to lose the last few lbs of fat on my stomach. My question is: is doing 45 minute bouts of cardio two to three times a day too much? What kind of adverse effects can occur?