Background: Substance use disorders (SUDs) constitute a serious medical problem. Information is scarce regarding the connection between SUDs and cardiovascular complications. We sought to examine the types of SUDs and their relationships with complications in patients with cardiovascular diseases. Methods: The present descriptive cross-sectional study evaluated 406 adult cardiovascular patients with 1 of the different types of SUDs according to eligibility criteria. Required data were extracted, recorded, and analyzed using the SPSS software, version 16. Results: The mean and standard deviation of the age of the participants was 59. 7±, 11. 92 years. Ninety percent of the participants used opium. Substance use had a significant relationship with age range, marital status, education level, and income (P<0. 05). Opium use was more frequent in patients with hypertension than other illegal substances (73. 8% vs 57. 1%,P=0. 035). Conclusions: Opium was the most frequent substance used by patients with cardiovascular disease. Moreover, our participants had little knowledge about the cardiovascular risks and complications related to SUDs. Therefore, stringent measures are recommended to prevent illegal substance use and raise public awareness in the country.