<jats:p>The thermal tolerance of marine decapod crustacea is defined through their capacities for oxygen uptake and distribution. High ambient CO<jats:sub>2</jats:sub> levels were previously shown to reduce hemolymph oxygen levels at enhanced cardiac performance during warming. This study investigated the impacts of warming under two CO<jats:sub>2</jats:sub> levels on ventilation and hemolymph circulation in edible crabs <jats:italic>Cancer pagurus</jats:italic>. It also highlights changes in the ventilatory and cardiac pauses displayed by Decapoda under routine metabolism. Animals were exposed to step-wise, sub-critical warming (12–20°C over 5 days) under control (470 μatm) and high (1,350 μatm) water <jats:italic>P</jats:italic>CO<jats:sub>2</jats:sub>. Flow-through respirometry was combined with magnetic resonance imaging and infra-red photoplethysmography to allow for simultaneous, non-invasive measurements of metabolic rates (<jats:inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mrow><mml:mover accent="true"><mml:mi>M</mml:mi><mml:mo>˙</mml:mo></mml:mover><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math></jats:inline-formula>), ventilation and cardiovascular performance. Crabs spent significantly more time in a low <jats:inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mrow><mml:mover accent="true"><mml:mi>M</mml:mi><mml:mo>˙</mml:mo></mml:mover><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math></jats:inline-formula> state (metabolic pause), when experiencing high CO<jats:sub>2</jats:sub> conditions above 16°C, compared to normocapnic warming. Heart rates leveled off beyond 18°C at any CO<jats:sub>2</jats:sub> level. Cardiac output continued to increase with high-CO<jats:sub>2</jats:sub>-warming, due to elevated cardiac stroke volumes. Consequently, temperature-dependent branchial hemolymph flow remained unaffected by CO<jats:sub>2</jats:sub>. Instead, a suppressing effect of CO<jats:sub>2</jats:sub> on ventilation was found beyond 16°C. These results indicate constrained oxygen uptake at stable cardiovascular performance in a decapod crustacean.</jats:p><jats:p><jats:italic>Cancer pagurus</jats:italic>: urn:lsid:zoobank.org:act:B750F89A-84B5-448B-8D80-EBD724A1C9D4</jats:p>