What are common side effects from the radioisotope in a myocardial perfusion scan?

None. There are no common side-effects from the radioisotope. There have been very rare reports of allergy. There is a theoretical, but unproven risk of the radiation inducing a cancer 10 to 20 years later. There also is a theoretical, but unproven risk of radiation myocarditis. The radiation exposure of 1 rem (about 10 msv ) has not been shown to be harmful. See http://sgoti.Ws/qmhwh7.
None. Since you are getting radioactive substances you shouldn't be pregnant or even hold an infant in you lap for 24 hours after the test. For this reason i avoid this test in women in the reproductive years if i can.