Purpose The purpose of this study was to assess the radiation dose and associated image noise of previously suggested calcium scoring protocols using dual-source CT. Methods One hundred consecutive patients underwent coronary calcium scoring using dual-source CT. Patients were randomly assigned to five different protocols: retrospective ECG-gating and tube current reduction to 4% outside the pulsing window at 120 (protocol A) and 100 kV (B), prospective ECG-triggering at 120 (C) and 100 kV (D), and prospective ECG-triggering at 100 kV with attenuation-based tube current modulation (E). Radiation dose parameters and image noise were determined and compared. Results Protocol A resulted in an effective dose of 1.3 ± 0.2 mSv, protocol B in 0.8 ± 0.2 mSv, protocol C in 1.0 ± 0.2 mSv, protocol D in 0.6 ± 0.1 mSv, and protocol E in 0.7 ± 0.1 mSv. Effective doses were significantly lower (P < 0.001) with 100 kV when compared to 120 kV protocols, and were significantly lower (P < 0.001) for prospective versus retrospective ECG-gating. No significant difference was found between protocol D and E. Significant negative correlations were found between the CTDI_vol and heart rate for both retrospective ECG-gating protocols (protocol A: r = −0.98, P < 0.001; protocol B: r = −0.83, P < 0.001). The mean image noise was 29.0 ± 6.7 HU, with no significant differences between the five protocols. The image noise was significantly correlated with the body weight (r = 0.21, P < 0.05) and BMI (r = 0.31, P < 0.01). Conclusions Effective dose of calcium scoring using dual-source CT ranges from 0.6 to 1.3 mSv. Prospective triggering and lower tube voltage significantly reduces the radiation but yield similar image noise.