Experiment with your search terms, i.e., try searching synonyms or alternative ways to express a concept. You also might include the terms "in vitro" and/or "animal model" with terms specific to your research. Also, rather than entering your all of your search terms in one search box as a statement or question, parse out the pieces of your research question into two or more search boxes and connect with an appropriate Boolean operator: AND, OR, NOT (sometimes AND NOT used instead of just NOT) as appropriate.
1) in vitro AND animal model and (heart OR cardiac OR cardiovascular)
2) animal model AND eating disorder*AND NOT rats (if you're seeking studies on other animals, but not rats)
3) animal model AND stress AND long term memory
4) animal alternatives testing AND rats AND "transient global ischemia"
Once you find relevant citations to articles, look at the search terms/subject headings assigned to those articles and try subsequent searches with various combinations of relevant search terms.
Use the HELP feature in any database if you're wondering if you're searching it effectively!