An EF below 30% is considered heart failure range and usually that reduces cardiac output to the degree that will cause shortness of breath, muscle fatigue, etc..
An enlarged heart is almost always secondary to heart failure, but it can be primary and cause heart failure and a low EF. Also, an enlarged heart, left ventricle, can cause arrhythmia, and the EKG indicates an incomplete BBB. An ICD is recommended and advisable.