Radionuclide angiography (RNA) permits analysis of contractility and conduction abnormalities. We determined the parameters of normal ventricular synchronization, assessed the reproducibility of the technique, and compared first harmonic (1H) and third harmonic (3H) analysis. Forty-four normal subjects (28 men and 16 women) were studied. RNA was performed in left anterior oblique (LAO) and left lateral (LL) projections. The onset (To), mean time (Tm), total contraction time (Tt) for right ventricle (RV) and left ventricle (LV), interventricular time (T(RV-LV) = Tm(LV - Tm(RV)) in LAO, and the apex-to-base time (T(a-b)) in LL were measured on the histograms of the time-activity curve. Reproducibility (R) was tested by studying 26 consecutive patients with two successive RNAs. RV starts contracting 25 ms before LV (To(RV) = 29 +/- 37 ms; To(LV) = 54 +/- 39 ms; mean +/- SD) with a 37 ms longer total contraction time. T(RV-LV) is 3 +/- 16 ms. In LL projection, apex and base contract synchronously: T(a-b) = 2 +/- 16 ms. 3H analysis enlarges all duration parameters (To, Tm and Tt), but does not alter synchronization (deltaT(a-b) and deltaT(RV-LV) between 1H and 3H <1%, p = NS). Reproducibility of the duration (T(tLV) and T(tRv)) and synchronization parameters (T(a-b) and T(RV-LV)) is high (R < or = 2.2%). In conclusion, the simultaneous contraction of right and left ventricles and of apex and base can be quantified by RNA phase analysis with high reproducibility. These results, consistent with published electrophysiological data, provide the basis for further non-invasive investigations of ventricular resynchronization in patients with basal electrical or mechanical asynchrony.