Background: Erectile dysfunction (ED) might be an early warning sign of blood vessel problems that can lead to heart attack. Men with a heart attack are more likely to have ED because of hemodynamic, neurohormonal and psychologic problems. We evaluated the frequency and cause of ED in patients who had AMI. Method: In 40 AMI patients, the presence of ED before and after MI was assessed by the abridged 5-item version of the International Index of Erectile Function (IIEF-5). The possible scores for the IIEF-5 range from 5 to 25, and ED was classified into five categories based on the scores: severe (5-7), moderate (8-16), mild (17-21), and no ED (22-25). Results: ED more than moderate was present in 21 (53%) and 33 (83%) patients before and after MI, respectively. The average frequency of sexual activity was decreased from 4.4 to 3.1 times/month after heart attack. The causes of the decreased sexual activity were ED (72%), dyspnea (11%), chest pain (11%) and fear for the heart attack (6%). There was no predisposing factor for the ED after MI. Conclusions: Heart attack can induce new development of ED and we need more study for the causes of ED.