A method for the accurate time domain characterization of Respiratory Sinus Arrhythmia (RSA pattern), is presented and applied on two groups of healthy subjects in order to lay the baseline of RSA patterns and to underlay their features: response to standing, stability in successive recordings and individuality of the shape of the RSA patterns. RSA pattern is evaluated by selective averaging of heart rate (HR) changes from multiple respiratory cycles over the respiratory phase and represents the complete modulating function of HR by respiration. The RSA pattern is evaluated with free respiration and even in cases of severe arrhythmia. Estimation error is 6-8% in magnitude, phase resolution is 0.2rad and sensitivity margin for respiratory related heart rate variability (HRV) components is 1%. RSA magnitude, phase lag, and expiration/inspiration time ratio are derived in addition to the entire pattern. In a group of 10 healthy young adults, a phase lag difference of 11.4±8.5% (mean±SD, p<0.004) was observed between supine and standing postures, possibly ascribed to breathing mechanics. A second group of 15 healthy young adults in supine rest showed stability of RSA pattern in successive recordings (several weeks apart) as well as individuality among subjects. This may suggest a non-scalar individual long term index for cardio-respiratory coupling. The method is complementary to the existing statistical and spectral methods. It allows the complete characterization of the primary RSA components and may open new insight into the effects of vagal activity and changes in clinical conditions.