This study evaluates whether YM443 causes any changes in the electrocardiogram of healthy adults.

Each subject participates in all four treatment periods separated by washout periods.

In order to maintain the blind between arms, all subjects will receive the same number of tablets per day in each period of either active drug or placebo.

Inclusion Criteria:

• Healthy Male or non pregnant, non lactating female
• Weighing at least 45 kg
• Body Mass Index (BMI) between 18 and 32 kg/m2

Exclusion Criteria:

• The subject has evidence of any cardiac conduction abnormalities
• The subject has a previous history of any medical or psychiatric condition that would preclude participation in the study
• The subject has participated in another clinical trial in the last 30 days
• The subject anticipates an inability to abstain from alcohol, or caffeine use, or from grapefruit and grapefruit juice from 48 hours prior to the administration of the first dose of YM443 on Day 1 of Period 1 and throughout the duration of the study
• The subject has used tobacco-containing products and nicotine or nicotine-containing products within six months prior to Screening
• The subject consumes more than 5 units of alcoholic beverages (one unit is 12 ounces of beer, 4 ounces of wine or 1 ounce of spirits) per week or has a history of substance abuse, drug addiction, or alcoholism within 2 years prior to Screening
• The subject has donated any whole blood or cellular blood component or has undergone significant loss of blood or has received transfusion of any blood or blood products within 56 days of Day -1 of Period 1 or has donated plasma within 7 days of Day -1 of Period 1