Edible crabs Cancer pagurus were subjected to acute severe hypoxia (15% air saturation). The cardiac responses were monitored with infra-red plethysmography (IR-PPG) and Magnetic Resonance Imaging (MRI).The oxygen partial pressure in the water was monitored using fibre-optic oxygen sensors. "PO2_record_IR-PPG_File_1" contains the recordings relevant for animals 1 (1st run), 3, and 4. "PO2_record_IR-PPG_File_2" contains the recordings for animals 1 (2nd run) and 2.IR-PPG recordings yielded heart rates as peak frequency. Data were also evaluated for signal peak area (integral, relative to a 1-minute minimum) and the average cyclic height as proxies for stroke volume changes.Cardiac MRI are from 4D (i.e. time-resolved 3D) stacks of images. The time series contains the entire contraction of one cardiac cycle. The volume stack covers the entire ventricle.