Many people inquire about health conditions of the Sussex when making an inquiry prior to purchasing one.  The following health concerns have been known to occur in Sussex Spaniels. Although to my knowledge, no  data has ever been collected  other than those conditions that are registered by the Orthopedic Foundation for Animals.  This information is my opinion based on research that I have completed and my experience with the breed.  

Don't  let this information scare you away from ever wanting to own a Sussex, most of these conditions are very rare. The ones with a asterick are the most common. 

After owning several breeds in the past,  I don't know how anyone could live without a Sussex in their life!  This page is for informational purposes only as all breeds of dogs have their own health concerns. 
There are 3 main Heart or Cardiac conditions that I could identify as ever occurring in Sussex. 
Pulmonic Stenosis 
This is the most single common valve problem seen.  This condition is a narrowing of the pulmonary valve opening that increases resistance to blood flow from the right ventricle to the pulmonary arteries.  It causes enlargement of the right side of the heart due to the heart muscle trying to  compensate for the increased work load.  Due to this occurring the right side of the heart can no longer pump effectively against the pulmonic valve and blood and fluid will begin to back up into the liver and abdomen.  This condition when identified is usually rated from 1-6 with 6 being the most severe. Many will survive a long normal life without treatments in less severe cases.  As the stenosis becomes worse the heart becomes weaker and life long medical management will be required. 
Patent Ductus Arteriosus (PDA)
PDA is a connection between the aorta and the pulmonary artery. The ductus arterious enables the blood to by-pass the lungs. During pregnancy this function is necessary because the fetus doesn't breathe air and doesn't need blood to circulated throughout the lungs to be oxygenated. It is however important at birth, when blood must flow to the lungs to be oxygenated. Normally the ductus closes very quickly after birth. If the ductus remains oxygenated blood intended for the body may be returned to the lungs, overloading the lungs blood vessels and unoxygenated blood will bypass the lungs and flow to the body.  AS a result heart failure will usually develop quickly. I have heard of surgery correcting this condition with good results. 
Tetralogy of Fallot
This is the third type of heart structure disorder that  has been seen in Sussex.  Tetralogy of Fallot is a combination of heart defects consisting of a large ventricular septal defect, displacement of the aorta that allows oxygen depleted blood to flow directly form the right ventricle to the aorta. There is also usually a narrowing of the outflow passage from the right side of the heart ( Pulmonic Stenosis), and a thickening of the wall of the right ventricle. Dogs affected with Tetralogy of Flallow will usually have a very loud murmur at birth, and will be cyanotic. Without surgical repair of these defects the life-span will be very short. 
Cataracts, Progressive Retinal Atrophy and Retinal Folds
These are all typical eye conditions that occur in most sporting dogs. Although I personally have not seen anything but retinal folds. Of these retinal folds none were of the type that would prevent registration with the Canine Eye Registration Foundation.
Joints *
DNA  *
Reproductive *

Bloat *
Gastric dilation-volvulus (GVD) 
This is a life threatening condition that occurs out of no where for seemingly no reason. The GDV syndrome is characterized by a rapid accumulation of air in the stomach. The dog will seem restless, not be able to become comfortable and may pace around. It is said that the stomach area becomes so taught that if tapped sounds like a drum. If the gastric dilation is not relieved promptly by giving a product such as Gas -X, passing a stomach tube, or surgical intervention the dog will normally not survive. There is no single cause why GVD occurs. An excellent article with the execption of the percent of raw food .Raw food is only 18-20% protein. THERE IS A HOMEOPATHIC REMEDY TO PREVENT BLOAT. CONTACT ME FOR INFORATION AND REMEDY.
PDP1 is a condition that affects both Sussex and Clumber Spaniels. This DNA test was identified in 1994 by Dr. Jesse Cameron of Canada.  PDP1 is known as the Exercise Intolerance Disease. It is a simple autosomal recessive trait,which means that both parents must carry the defective trait for the dog  to be Affected. Symptoms include cardiac, pulmonary and neurological complications that will result in a shorter life span of the dog that is Affected. 
Some studies suggest association of PDP1 deficiency with fetal and newborn mortality. Disease progression can be slowed by dietary changes and supplementation. A diet high in protein fats and free of carbohydrates will help. Also  adding the supplements  Amino Acids and Co Q10 is recommended. Dogs that are only Carriers of the PDP1 will remain unaffected as well as those that are Clear of PDP1.

PDP1 can be identified with the use of DNA Cheek swabs and/or blood samples. If you are talking with a breeder that does not test for PDP1 - run do not walk away.  This can be eliminated through testing and careful breeding programs. One must know what results are prior to being able to breed selectively. 

Pyruvate Dehydrogenase Phosphatase1 Deficiecy ( PDP1)
Hip and Elbow dysplasia are a common occurrence in Sussex Spaniels. This does not mean that they will be lame or have an early on set of joint problems. In most cases you will never know that an dog is dysplastic until you have completed x-rays and they do not pass the Orthopedic Foundation for Animals. .There was a time just recently back in 1997 when there wasn't a Sussex registered nor tested for hip dysplasia. Many more breeder's are testing now than ever before and this is a great thing.  
Elbow and Hip Dysplasia
Let's Have Puppies
Midline  *
Cleft Palates, Unbiblical Hernia's and Retained Testicles
Although these conditions are easily detected they tend to be prevalent in Sussex ,I believe that these can be related directly back to  the over use of vaccines and chemicals such as Heartworm medications and Flea/Tick products. I also believe that diet plays a role as well.  Since I am now on my 4th generation of Natural Rearing I am seeing a 75 % drop in unbiblical hernia's. I have not ever had the experience of a retained testicle thus far. It is my firm believe that Cleft Palates are a nutritional deficiency
If the main reason you want a Sussex is because it is a rare breed and puppies may have a higher price than other breeds, think again.  Sussex have a multitude of problems ranging from infertility to survival rate of puppies. We have been very blessed with the large litters. We have also had several singleton litters and missed breedings. The majority of breeder's will automatically c-section because of uterine inertia. They may also start testing progesterone levels at 1 month due to progesterone not maintaining through pregnancy, causing re-absorbed litters and/or miscarriages.  Maybe one of the reasons that Sussex have never become popular is because they are not consistent in reproducing. Reproductive problems do not appear to be related to hypothyroidism. I believe it is related to a small gene pool, over vaccinating, insufficient diets and use of chemicals. 
There are far to many cancers in all dogs. The Sussex seem to have problems with Oral Cancer, which is a very aggressive cancer and tumors on the spleen, which is a slower growing form of cancer.  It's just another reason to confirm  that Natural Rearing is the right thing to do. Elimination of all toxins that are normally put on (Flea/Tick control ), ingested (Heartworm medicines) or  injected into their bodies (vaccines). There are alternative's to these products. Live and Learn!  Our Thrive page has a lot of good information and is a good place to begin. 
Anesthesia *
Sussex Spaniels are very sensitive to different  types of anesthesia.. 
Health Concerns of the Sussex Spaniel