This paper presents an empirical analysis about how the Nielsen's usability heuristics are perceived by novice evaluators. Twenty-eight undergraduate students of an Informatics Engineering program were trained in usability and heuristic evaluations for this purpose. They were asked to perform a heuristic evaluation of a transactional Web site. A survey was taken in order to capture their perceptions about the usability heuristics. The design of the survey was focused on determining evaluators' perceptions about six dimensions: ease of use, usefulness, clarity, checklist necessity, intention to use and completeness. Analyzing the results, we could determine that all the above mentioned constructs have an influence in the intention to use the heuristics in future usability evaluations, excepting the perceived clarity. Based on the obtained results, a perception-based model of the usability heuristics is presented.