The aim of these statistical notes was to give the cardiologist the suitable tools for the understanding of the statistical aspects in the reading of papers presenting the results of randomized controlled clinical trials, in the most simple and intuitive way, without any previous knowledge of basic statistics. The fundamentals of the most common tools for the comparison of two experimental treatments, are developed by getting cue from classical cardiological examples and by guiding the reader, step by step, toward the understanding and critical discussion of the proposed examples. In particular, this note focuses the attention on the main "indicators" of absolute and relative effect measures by evidencing their most important differences.