Heavy drinking can also cause cardiomyopathy, a potentially deadly condition in which the heart muscle weakens and eventually fails, as well as heart rhythm abnormalities such as atrial and ventricular fibrillation. Atrial fibrillation, in which the heart's upper chambers (atria) twitch chaotically rather than constrict rhythmically, can cause blood clots that can trigger a stroke. Ventricular fibrillation causes chaotic twitching in the heart's main pumping chambers (ventricles). It causes rapid loss of consciousness and, in the absence of immediate treatment, sudden death.