Heart Failure
Heart failure causes shortness of breath and fatigue that tends to increase with physical exertion. Heart failure also can cause swelling in the feet, ankles, legs, abdomen, and veins in the neck.
Arrhythmia
Some arrhythmias can cause your heart to suddenly stop beating. This condition is called sudden cardiac arrest (SCA). SCA causes loss of consciousness and death if it's not treated right away.