Abstract: The Cardiac Output (CO), Filling Time (FT) and Myocardial Performance Index (MPI) derived optimal atrioventricular delay (AVD), were compared and systolic and diastolic performance at every optimal AVD were analyzed. Thirty-two patients with implanted DDD pacemaker were investigated from implantation time to 6 months following PM implantation, in Cardiovascular Research Center of Tabriz University of Medical Sciences. The evaluation was performed during AV sequential pacing with different programmed AVDS ranged from 100 to 200 msec by steps of 20-30 msec. At every AVD, the following parameters were measured: FT, mitral VTI, ET, aortic VTI, ICT and IRT. CO and FT derived optimal AVDs were significantly different (146±37 and 126±35 msec, respectively), but their difference with MPI derived optimal AVDs was not significant (130±28 msec). ICT/ET was similar at CO, FT and MPI derived optimal AVD (0.24±0.10, 0.22±0.05 and 0.20±0.07, respectively). IRT/ET ratio was similar at CO, FT and MPI derived optimal AVDs (0.46±0.14, 0.45±0.10 and 0.42±0.10, respectively). Different methods indicate different optimal AVDs. However analysis of systolic and diastolic performance shows that different AVDs result in similar systolic or diastolic performance. At MPI optimized AVD, a high CO combined with the most advantageous conditions of both isovolumic contraction and relaxation phases is achieved.