Mediates nucleation of actin filaments and thereby promotes actin polymerization (PubMed:18403713, PubMed:25250574, PubMed:26370058, PubMed:26417072). Plays a role in the regulation of actin filament length (By similarity). Required for normal sarcomere organization in the heart, and for normal heart function (PubMed:18403713). {ECO:0000250|UniProtKB:Q3UHZ5, ECO:0000269|PubMed:18403713, ECO:0000269|PubMed:25250574, ECO:0000269|PubMed:26370058, ECO:0000269|PubMed:26417072}. This is the function of LMOD2 (leiomodin 2, ENSG00000170807).