We present high-resolution Hα rotation curves of four late-type dwarf galaxies and two low surface brightness (LSB) galaxies, for which accurate H I rotation curves are available from the literature. Observations are carried out at Telescopio Nazionale Galileo. For LSB F583-1 an innovative dispersing element was used, the Volume Phase Holographic, with a dispersion of about 0.35 Å pixel-1. We find good agreement between the Hα data and the H I observations and conclude that the H I data for these galaxies suffer very little from beam smearing. We show that the optical rotation curves of these dark matter-dominated galaxies are best fitted by the Burkert profile. In the centers of galaxies, where the N-body simulations predict cuspy cores and fast rising rotation curves, our data seem to be in better agreement with the presence of soft cores.