1.1. Recovery of beating in ventricles of the bivalves Modiolus demissus demissus (Mdd) and Modiolus demissus granosissimus (Mdg), arrested by hypoosmotic seawater, is accelerated by 340 atm.2.2. Pressure does not accelerate recovery of rhythmicity by accelerating the volume regulatory amino acid efflux.3.3. Pressure greater than 200 atm accelerates onset of quiescence in Mdd exposed to Ca-Mg-free artificial seawater.4.4. Tachycardia, induced by divalent ion-free seawater at 1 atm, is suppressed by 340 atm.