The zebrafish is a well established model of vertebrate development, but has recently emerged as a powerful tool for cardiovascular research and in vivo cardiovascular drug discovery. The zebrafish embryo's low cost, small size and permeability to small molecules coupled with the ability to generate thousands of embryos per week, and improved automation of assays of cardiovascular development and performance allow drug screening for a number of cardiovascular effects. Such studies have already led to discovery of novel cardiovascular drugs with potentially clinically beneficial effects. In this review we summarise the advantages and disadvantages of the zebrafish for drug discovery using some patents, previous literature on zebrafish-based drug screening and assess where the zebrafish will fit into existing drug discovery programmes.