BACKGROUND Premature ventricular contraction (PVC) is one of the most common kinds of arrhythmias for which the treatment falls into dilemma. Previous clinical application showed that the traditional Chinese Medicine Shensongyangxin (SSYX) capsule is efficacious for the treatment of PVCs. This randomized clinical trial aimed to further evaluate the efficacy and safety of SSYX capsule on treating PVC. METHODS The subjects who had frequent PVCs with or without organic heart disease and normal cardiac function were enrolled in the study. The primary endpoint was the change of PVC numbers after eight-week medication with SSYX capsule. The secondary endpoints included change of clinical symptoms related to PVCs and the safety evaluation of SSYX capsule. Totally 188 PVC patients were randomly enrolled in the non-organic heart disease PVCs trial and orally took either SSYX capsules or analogues (three times per day, 4 capsules one time). A total of 671 PVCs patients were randomly enrolled in the organic heart disease PVCs trial, and orally took either SSYX capsules (three times per day, 4 capsules one time) or mexiletine tablet (three times per day, 150 mg one time). The PVCs were monitored and calculated with 24-hour Holter electrocardiogram. Routine blood, liver and kidney function were tested before and after medication with SSYX capsule. RESULTS SSYX capsules significantly decreased the PVCs numbers and alleviated the related symptoms in patients with or without organic heart disease. In non-organic heart disease group, SSYX capsules and the placebos decreased the PVCs from 12,561.34 ± 9,777.93 to 4,806.87 ± 6,507.17, and 12,605.69 ± 8,736.34 to 10,364.94 ± 9,903.41, respectively. The total effective rate was 74.2% and 28.9% in SSYX and placebo groups (P < 0.001). In organic heart disease group, SSYX capsule and mexiletine decreased the PVCs from 8,641.01 ± 8,923.57 to 3,853.68 ± 7,096.42, 8,621.61 ± 8,367.74 to 5,648.29 ± 8,667.38, respectively. The total effective rate was 65.8% and 50.7% in SSYX and mexiletine groups (P < 0.001). In addition, SSYX capsule significantly alleviated PVCs-related symptoms such as palpitations, chest tightness, insomnia, fatigue, and night sweats. No adverse cardiac events were observed except some slight gastrointestinal side effects during the study. CONCLUSIONS Compared with placebo or mexiletine, SSYX capsules have significant therapeutic efficacy in reducing PVCs numbers and alleviate PVCs-related symptoms.