Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 05, 2020
Cover [Abstract]
Entity Registrant Name	ARCA Biopharma, Inc.
Entity Central Index Key	0000907654
Entity Current Reporting Status	Yes
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Period Focus	Q1
Trading Symbol	ABIO
Document Fiscal Year Focus	2020
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		1,594,070
Entity Shell Company	false
Entity File Number	000-22873
Entity Tax Identification Number	36-3855489
Entity Address, Address Line One	11080 CirclePoint Road
Entity Address, Address Line Two	Suite 140
Entity Address, City or Town	Westminster
Entity Address, State or Province	CO
Entity Address, Postal Zip Code	80020
City Area Code	720
Local Phone Number	940-2200
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes