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Document And Entity Information (USD $)
 12 Months Ended
Dec. 31, 2011
Mar. 23, 2012
Jun. 30, 2011
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2011    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2011    
Entity Registrant Name ARCA biopharma, Inc.    
Entity Central Index Key 0000907654    
Current Fiscal Year End Date --12-31    
Entity Filer Category Smaller Reporting Company    
Entity Common Stock, Shares Outstanding   12,182,999  
Entity Well-known Seasoned Issuer No    
Entity Public Float     $ 14,193,288
Entity Current Reporting Status Yes    
Entity Voluntary Filers No