INTRODUCTION Diagnostic tests that use ionizing radiation play a central role in cardiology and their use has grown in recent years, leading to increasing concerns about their potential stochastic effects. The aims of this study were to compare the radiation dose of three diagnostic tests: single photon emission computed tomography (SPECT), invasive coronary angiography (ICA) and cardiac computed tomography (cardiac CT) and their evolution over time, and to assess the influence of body mass index on radiation dose. METHODS We assessed consecutive patients included in three prospective registries (SPECT, ICA and cardiac CT) over a period of two years. Radiation dose was converted to mSv and compared between the three registries. Differences over time were evaluated by comparing the first with the fourth semester. RESULTS A total of 6196 exams were evaluated: 35% SPECT, 53% ICA and 22% cardiac CT. Mean radiation dose was 10.7±1.2 mSv for SPECT, 8.1±6.4 mSv for ICA, and 5.4±3.8 mSv for cardiac CT (p<0.001 for all). With regard to the radiation dose over time, there was a very small reduction in SPECT (10.7 to 10.5 mSv, p=0.004), a significant increase (25%) in ICA (7.0 to 8.8 mSv; p<0.001), and a significant reduction (29%) in cardiac CT (6.5 to 4.6 mSv, p<0.001). Obesity was associated with a significantly higher radiation dose in all three exams. CONCLUSIONS Cardiac CT had a lower mean effective radiation dose than invasive coronary angiography, which in turn had a lower mean effective dose than SPECT. There was a significant increase in radiation doses in the ICA registry and a significant decrease in the cardiac CT registry over time.