The ZESCA Trial will directly compare the efficacy and safety of bupropion versus placebo as a means of reducing smoking rates in patients following an ACS. The ZESCA Trial will be a multi-center effort, coordinated from the Jewish General Hospital/McGill University (Montreal, Quebec). A total of 1500 patients will be randomized following an ACS but before hospital discharge via an Internet web site. Prior to the start of the treatment, patients in both treatment arms will receive a standard physician-administered counseling session regarding smoking cessation. Patients will begin treatment in-hospital and will be monitored in-hospital for ≥ 2 days prior to discharge. Half the patients will receive bupropion for 9 weeks and the other half will receive placebo pills for 9 weeks. Patients receiving bupropion will take 150 mg once per day for 3 days and then 150 mg twice per day for the remainder of 9 weeks. Prior to discharge, the patients will receive an information sheet listing the possible side effects of bupropion. They will be advised to consult the treating physician should they experience any listed side effects. While in-hospital, patients will have quit smoking and they will be instructed to not restart smoking when discharged. Phone calls to the patients will be made by the study nurses at weeks 1 and 2 of the 9-week treatment period. In addition, the patients will have clinic visits at weeks 4 and 9 as well as months 6 and 12. Smoking abstinence will be assessed at 4 weeks, 9 weeks, 6 months, and 12 months after randomization. Smoking abstinence will be defined as the complete abstinence in the week prior to the clinic visits and levels of exhaled carbon monoxide ≤ 10 ppm. Side effects of bupropion in patients following ACS as well as clinical events following initiation of treatment will be measured at weeks 1-8 (by telephone calls), and weeks 4 and 9 as well as months 6 and 12 (by clinic visits). Withdrawal symptoms will also be assessed by the nurses during their weekly calls.