Document and Entity Information	3 Months Ended
	Mar. 31, 2015	May 11, 2015
Document And Entity Information [Abstract]
Entity Registrant Name	ARCA Biopharma, Inc.
Entity Central Index Key	0000907654
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2015
Document Fiscal Period Focus	Q1
Trading Symbol	ABIO
Document Fiscal Year Focus	2015
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		21,198,411