To evaluate whether lazabemide has proarrhythmic or hypotensive potency in Parkinson's disease (PD), we conducted an 8-week, double-blind, placcbo-controlled, parallel group study with use of 24-hour ambulatory electrocardiographic (ECG) monitoring. Fifty-one patients with PD who did not have clinically apparent heart disease were randomized in a double-blind fashion to receive either lazabemide (n = 25) or placebo (n = 26) treatments. Lazabemide therapy did not induce clinically significant arrhythmias. A paroxysmal atrioventricular (AV) block, which progressed from first-degree AV block, was found in one patient in the lazabemide group. This was determined not to be a new AV block. However, the causality of lazabemide in prolongation of the pause was not ruled out completely. In addition, the asymptomatic fall in systolic blood pressure seen 3 minutes after standing up was observed to be more pronounced in the lazabemide group than in the placebo group. The mean decrease of systolic blood pressure was 10 mmHg greater in the lazabemide group than in the placebo group. In conclusion, lazabemide did not induce any clinically significant arrhythmias in patients without clinically apparent heart disease. However, it may increase the asymptomatic, orthostatic drop in systolic blood pressure.