Together, these data indicate that Smyd1b is required for F-actin myofibril organization in cardiomyocyte, and Tg(myl7:Lifeact-GFP)mb21 transgenic zebrafish are a useful model to analyze F-actin myofibril defects in cardiomyopathy. The gene discussed is MYL7; the disease is cardiomyopathy.