Lasix can sometimes decrease the excretion of
lithium in the kidneys, but if your physician monitors your
lithium levels it should be fine. Lithium toxicity can cause a slow heart rate and other cardiac arrhythmias, but these aren't common. As for your son, it sounds as if his heart conditions were genetic and not caused by anything you may or may not have done. Please don't feel responsible for his death. I hope this helps.