<prompt> Canon A wave is seen in:Atrial fibrillationComplete heart blockVentricular fibrillationMobitz 1 heart block  <response>: Ans. b Complete heart blockRef.-.Harrison 18th edition, chapter 227: The a wave reflects right atrial presystolic contraction and occurs just after the electrocardiographic P wave, preceding the first heart sound Sj. The a wave is not present with atrial fibrillation. Canon a wave occurs with Atrioventricular AV dissociation complete heart block due to right atrial contraction against a closed tricuspid valve. Wide complex tachycardia like ventricular tachycardia A prominent a wave is seen in patients with reduced right ventricular compliance like Right ventricular failure. 