Background: An anomalous origin of the right coronary artery from pulmonary artery (ARCAPA) is a very rare coronary anomaly. Case summary: A 56-year-old man, presenting haemodynamically unstable due to very rapid atrial fibrillation, was found to have ARCAPA by coronary computed tomography angiography. He had normal left ventricular ejection fraction and without reversible ischaemia on an adenosine stress rubidium positron emission tomography. He was treated solely with betablockers and has been well since. Discussion: Numerous case reports on ARCAPA have previously been published, but no previous reports have found rapid atrial fibrillation to be the primary symptom of presentation. Current evidence level concerning the treatment is low; nevertheless, surgical intervention should always be considered to prevent sudden cardiac death. The patient in this case was offered surgical intervention but declined.