Magnetic resonance imaging is a diagnostic technique widely used in medicine and showing a growing impact in cardiology. Biological effects associated to magnetic resonance electromagnetic fields have received far little attention, but it cannot be ruled out that these fields can alter DNA structure. The present study aimed at to identify possible DNA damage induced by magnetic resonance scan in humans. Lymphocyte cultures from healthy subjects had been exposed into magnetic resonance device for different times and under different variable magnetic exposure in order to build dose-effect curves, using micronuclei induction as biological marker. Replicate cultures were also left for 24h at room temperature before stimulation, to verify possible damage recovery. Furthermore, micronuclei induction and recovery up to 120h have been also evaluated in circulating lymphocytes of individuals after cardiac scan. A dose-dependent increase of micronuclei frequency was observed in vitro. However after 24h, the frequency returns to control value when the exposure is within diagnostic dosage. After in vivo scan, a significant increase in micronuclei is found till 24h, after the frequencies slowly return to control value.