BACKGROUND: Spinal muscular atrophy (SMA) is a genetic neuromuscular disease associated with cardiovascular abnormalities. The impact of nusinersen treatment on myocardial function in children with SMA remains unclear. This study aimed to evaluate changes in left ventricular (LV) function in children with SMA before and after nusinersen treatment using echocardiography. METHODS: A prospective observational study was conducted on 35 children with SMA who received six doses of nusinersen within 10 months at a tertiary hospital in China. 35 healthy controls were included for comparison. LV function was assessed using echocardiography at baseline and after 10 months of treatment. LV dyssynchrony and myocardial strain were measured using two-dimensional speckle tracking echocardiography. RESULTS: The mean age of the SMA children was 6.58 ± 3.11 years. Before treatment, the global longitudinal strain (GLS) in the SMA group was significantly lower than in the control group (p <
0.001), and LV systolic synchronization was poorer (p <
0.001). Following nusinersen treatment, GLS increased (p <
0.001) and synchrony improved (p = 0.004) in the SMA group. However, even after 10 months of treatment, GLS in the SMA group remained lower than in the control group (p = 0.011), and LV synchronization was still inferior (p = 0.028). CONCLUSIONS: Short-term nusinersen treatment improved LV function in children with SMA, as evidenced by changes in LV myocardial strain indicators. Further research is warranted to explore the treatment of myocardial injury in SMA patients.