Background <p>To evaluate the effect of heat-assisted obturation on the distribution of filling material within apical and coronal lateral canals, the composition of the filling materials present within these canals, and the radiographic and microscopic characteristics of the premixed calcium silicate–based endodontic sealer after setting in standardized lateral canals.</p> Methods <p>Sixty simulated root canals with standardized apical and coronal lateral canals (<i>n</i> = 120) were prepared in resin blocks. Canals were obturated using either a single-cone technique or carrier-based technique, both combined with a premixed calcium silicate–based sealer (CeraSeal^®). Radiographic and microscopic analyses were performed immediately after obturation and after complete sealer setting (4 days, 37&#xa0;°C, 100% humidity). Lateral canal filling was classified according to obturation completeness and material composition. Statistical analysis was performed using chi-square, Fisher’s exact, and McNemar tests (α = 0.05).</p> Results <p>Heat-assisted obturation resulted in significantly higher rates of complete filling in apical lateral canals compared with the single-cone technique (90% vs. 46.7%, <i>p</i> &lt; 0.001). Coronal lateral canals exhibited lower filling rates regardless of technique. Microscopic analysis showed that heat-assisted obturation promoted the combined presence of gutta-percha and sealer within lateral canals, whereas the single-cone technique resulted exclusively in sealer penetration (<i>p</i> &lt; 0.001). No significant differences were observed between immediate and post-setting evaluations (<i>p</i> = 1.0).</p> Conclusions <p>Heat-assisted obturation enhanced the distribution of filling materials within standardized lateral canals and promoted the concomitant presence of gutta-percha and sealer. No radiographic or microscopic differences were observed between the immediate and 4-day evaluations.</p>