Cardiomyopathy syndrome is a slowly developing serious cardiac disease culminating in acute death affecting large Atlantic salmon in good body condition and close to harvest size. Heart and skeletal muscle inflammation (HSMI) is a serious viral disease of Atlantic salmon. HSMI is caused by a naked double-stranded RNA-virus called piscine orthoreovirus. Pancreas disease is a serious viral disease of farmed Atlantic salmon, rainbow trout and brown trout. Some bacterial and fungal diseases may occasionally cause severe cardiac disease in salmonids, and in cleaner fish used for delousing salmon in aquaculture farms. The significance of cardiac diseases in farmed salmonids is not restricted to acute mortality; chronic manifestations may result in poor growth and reduced capacity to handle stressful management operations like handling, transport and treatments. Larval trematodes and several protozoans may be associated with cardiac disease, particularly in wild fishes.