Constipation and megacolon are important problems in the domestic cat, and many cats will require invasive surgery (i.e., colectomy) if medical treatments fail. Experiments performed in our laboratory in 1995 showed that cisapride was a potentially effective colonic prokinetic agent in healthy cats and in cats affected with constipation and idiopathic megacolon. Cisapride was used successfully by feline practitioners for about five years before it was discontinued by the manufacturer in July 2000. Consequently, there is a need for new drugs to treat this disease. This study will test two new drugs that have efficacy in humans as potential treatments for cats with megacolon.