We studied the relationships of electrical and mechanical synchronization in patients with heart failure (CHF) and various degree of ventricular conduction delays. Ninety-two CHF patients (60 +/- 13 years old, LVEF < 45%), NYHA II-III-IV, and 35 age-matched control subjects were studied with angioscintigraphic phase analysis. We measured ejection fractions (LVEF, RVEF) and calculated the total activation time for the left (TtLV) and right ventricle (TtRV), and the synchronization time between right and left ventricle (TRVLV), and between LV apex and base (Tab). Patients were divided into three groups according to QRS duration: group 1 < 120 ms (n = 28), group 2 < 150 ms (n = 23), group 3 > or = 150 ms (n = 41). In group 1: LVEF = 31.1 +/- 10.9%, RVEF = 30.1 +/- 12.6%, TtLV = 204 +/- 70 ms, TtRV = 183 +/- 61 ms, TRVLV = 7 +/- 33 ms, Tab = 29 +/- 23 ms. In group 2, these were: 27.8 +/- 9.1%, 27.8 +/- 8.8%, 227 +/- 95 ms, 248 +/- 137 ms, 35 +/- 42 ms*, and 39 +/- 53 ms respectively. In group 3: LVEF = 20.5 +/- 9.5%t, RVEF = 28.4 +/- 16.1%, TtLV = 304 +/- 155 mst, TtRV = 234 +/- 106 mst, TRVLV = 64 +/- 42 mst, and Tab = 67 +/- 48 ms*, all P < 0.001 versus controls *P < 0.05 versus G1, tP < or = 0.01 versus G1. A significant relation links QRS to both inter- and intraventricular asynchrony (TRVLV: r = 0.65; TtLL: r = 0.70, Tab: r = 0.60), and to LV function (r = 0.72); while LVEF relates more closely to intraventricular asynchrony: TtLV (r = 0.52), TtLL (r = 0.67), than to interventricular asynchrony: TRVLV (r = 0.48); P < 0.01, P < or = 0.001. In CHF patients, electromechanical and contractile alterations are coupled; regional activation may be an early parameter allowing the detection of ventricular dyssynchronization.