Melatonin did not significantly change heart rate in this study: http://jap.physiology.org/cgi/content/abstract/91/3/1214 Mentioned because there was the earlier assumption elsewhere that melatonin would slow the heart rate. (There are a lot of studies on melatonin and the heart health and so far I not encountered any negative ones. Lupron is another matter on that score so when in doubt it may pay to check heart health before using Lupron.) BTW, enlargement of the heart happens slowly over time in response to heart disease, and is not a suddenly acquired condition. -- Sukie (not a vet) Ferret Health List co-moderator http://www.smartgroups.com/groups/ferrethealth FHL Archives fan http://ferrethealth.org/archive/ replacing http://fhl.sonic-weasel.org International Ferret Congress advisor http://www.ferretcongress.org [Posted in FML issue 5033]