Real-world data on the efficacy of mavacamten, indicated for the treatment of obstructive hypertrophic cardiomyopathy (oHCM), are relatively scarce, particularly in patients with extreme left ventricular outflow tract (LVOT) gradients and concerning its short-term effects. We investigated a cohort of twenty-five oHCM patients [15 men (60 %), mean age: 55 ± 11 years], with a resting or provoked LVOT gradient of >100 mmHg, receiving mavacamten treatment. Patients underwent a complete standard and 2D-speckle tracking echocardiographic examination after one week (W1) of treatment initiation and at subsequent four-week intervals. After only one week of mavacamten therapy, both the resting peak LVOT gradient (from 121 to 87 mmHg) and the Valsalva gradient (from 167 to 129 mmHg) significantly decreased (all p < 0.001), showing further decrease (resting gradient: to 67 mmHg at W4, and to 56 mmHg at W8; Valsalva gradient to 102 mmHg at W4, and to 80 mmHg at W8, all p < 0.001). NTproBNP levels also significantly decreased already at W1 (-1467 pg/ml), showing further decrease during treatment (-1735 pg/ml at W4, and - 2048 pg/ml at W8; all p < 0.001). NYHA functional class, 6-min walk distance, parameters of myocardial work and many of the assessed diastolic parameters showed significant improvements and no change in LV ejection fraction or global longitudinal strain was observed. Mavacamten effectively reduced even >100 mmHg LVOT gradients and led to significant gradient reduction already in one week. Besides favourable changes in LVOT obstruction, structural and functional echocardiographic parameters, functional capacity, and cardiac biomarkers, it also led to significant improvement in myocardial work parameters.