Taken from The Rottweiler Club of Canada:  

Heart Disease

Rottweilers are a breed which has a high incidence of an abnormal heart sound, or murmur, caused by Subaortic stenosis (SAS). When you use an ordinary garden hose (without a nozzle) the water flows out quietly; when you cover part of the hose with your finger, it causes a disruption of the water flow and a lot of noise. If the heart is working normally, there are few sounds (except the pumping sound) but if something causes a disruption of the blood flow, a murmur occurs. A narrowing of the heart, a stenosis, just below the aortic valve, results in an abnormal sound, the murmur. SAS is the second most common congenital heart defect in the dog, and the Rottweiler has a higher occurrence than most other breeds. It is a clue to a veterinarian that there is something wrong. This condition is heritable and should be addressed, with the following information in mind. Heart murmurs are graded on a scale of 1 to 6, with one being very mild and six being very serious Murmurs can exist due to a large number of heart problems ( infection, trauma, anemia, etc.) and some murmurs are innocent, meaning that no cardiac pathology exists. Discussions with Dr. M. O'Grady, Dipl. ACVIM ( Cardiology ) at the Ontario Veterinary College and Dr. D. Brummer Dipl. ACVIM, of the Orchard Park Veterinary Medical Center, as well as the article by Dr.W.A. Brown, Dipl. ACVIM ( Cardiology ) in the Third Quarter of the 1997 MRC Newsletter, entitled " Canine Subvalvular Aortic Stenosis " provided me with the following information. Mild heart murmurs in puppies less than 20 weeks of age are to be noted only and are not an immediate cause for concern. Some of these will be innocent, some may be a result of a minor problem, and some of these can and do disappear with age. A serious murmur in a young pup is definitely significant and a murmur which persists past 20 weeks of age should then become a cause for concern. The health status of the puppy and the advice of the veterinarian may warrant investigative procedures in order to give a prognosis. Auscultation of the heart (with a stethescope) in an adult dog over the correct area of the chest could lead to a presumptive diagnosis of SAS, if a murmur were present. The problem with SAS is that a dog can be a carrier and never be diagnosed even with the current available veterinary techniques. " Distinguishing murmurs caused by mild SAS from functional (innocent ) murmurs can be dificult and sometimes impossible, " ( Dr. Brown ) If a dog has SAS, it may be detected on auscultation, on echocardiography,on Doppler or on a post-mortem by a qualified pathologist. However, it can be a very difficult ante-mortem (alive) diagnosis. The carrier state means that the dog itself is normal, but can produce the defect in its offspring (genes). Until genetic markers are available for this problem, we are unable to identify carriers prior to breeding. " Innocent murmurs are most common in young growing dogs.The prevalence of innocent murmurs in the adult dog population is unknown. " ( Dr. Brown ) If a murmur is heard on auscultation, and warrants further investigation, it is then appropriate to seek the services of a specialist in cardiology. It is at this point that sophisticated diagnostic procedures will be recommended. Echocardiography is like an ultrasound of the heart and allows the cardiologist to see if the anatomy and function of the heart are normal. " A two-dimensional echocardiogram study ( without Doppler, the ultimate in cardiovascular testing ) is not sufficiently sensitive to exclude a diagnosis of mild SAS" ( Dr. Brown ) It is therefore suggested that a cardiac examination for the determination of mild SAS include two dimensional, m-mode and Doppler studies.( Suffice it to say that this is a very detailed study of a dogs' heart. ) The results of the cardiac examination can be; a) Negative on auscultation ...means that a murmur is not present at rest and therefore most dogs will be free of SAS. ( may still be a carrier ) b) Positive on auscultation...means that a murmur is present which may be innocent or a sign of congenital heart disease. As innocent murmurs are generally mild, those dogs with a murmur of Grade 3 or more will likely have congenital heart disease 1) Positive on echocardiogram...is a definite diagnosis of SAS 2) Negative on echocardiogram... the murmur may be innocent or mild SAS may be present Dr, Brown : " Presently we lack the ability to reliably identify all carriers or mildly affected dogs with SAS. Until molecular markers or some other highly specific test is developed it will be impossible to eliminate these dogs from the breeding pool. " The OFA has established a Congenital Heart Registry whose guidelines were established by veterinary cardiologists. A dog at 12 months of age, which auscultates normally is considered to be free of congenital heart disease Upon confirmation of this, the OFA will issue a certificate. Although the OFA prefers the expertise of a cardiologist ( to perform the auscultation), a letter from any veterinarian is acceptable. This is in contrast to a CERF certificate, which is performed only by veterinary ophthamologists. ( A veterinary cardiologist has endured extra years of training, and has acquired a degree, Diplomate of the American College of Veterinary Internal Medicine, Cardiology or ACVIM (cardiology), whereas an ophthamologist has acquired the degree, American College of Veterinary Ophthamologists, ACVO, both are prestigious academic titles). A cardiologist, is more likely to auscultate a murmur than a regular veterinarian. The Congenital Heart Registry certificiate states the age of evaluation and one of the letters "C" for cardiologist, "S" for specialist, an ACVIM with an interest in another field ( i.e. neurology ) or "P" for private practitioner. Now, what does all this imply? I would suggest that any negative response to a mild heart murmur in a dog less than 20 weeks of age is premature and unfounded. If an adult dog of merit is found to have a murmur, it should be investigated by a cardiologist as to the exact diagnosis and consequential impact on the breed. If a veterinary report for cardiac evaluation is presented for review to a breeder, it should be carefully examined as it may state that "SAS is not ruled out by this exam". I have seen such a statement on a cardiac evaluation form from a veterinarian who is an ACVIM certified cardiologist. This statement is a result of the difficulty in diagnosing SAS, as previously discussed.. If you currently breed rottweilers, you can produce SAS no matter what you have done to try to prevent this problem. ( i.e. two phenotypically normal "carriers" bred together. ) If puppies have mild SAS, do they have to be euthanized? Absolutely not! Many will lead a normal life. A dog may fail a cardiac evaluation under one veterinarian but pass under another and still be advertised as "cardiac clear", I've seen it done. One of our two stud dogs, Jack, prior to us including him in our breeding program, was given a thorough veterinary examination, including clinical examination, auscultation, blood work, fecal, heartworm, thyroid and sperm evaluation at the Veterinary Teaching Hospital at Michigan State University. We would not have considered him as a stud dog for our kennel, if he had clinical evidence of SAS, and yet I have no heart certificate for him. He has had no problems to my knowledge, in his numerous breedings, except for one case in which I have received no concrete evidence of substantiated cardiologist examination after the age of 5 months !!! As well, Draviet, our other stud dog, has been auscultated by myself and by at least two of my Associates, is free of any audible heart murmur and yet I have no heart certificate for him. Should I obtain one? If a phenotypically OFA "good" male is breed to a phenotypically OFA "good" female and two pups are dysplastic out of ten, should the parents of these offspring be neutered or is this an acceptable rate of occurrence? What if all the pups had excellent stable temperaments, a definite aim and priority in our breed. Similarly, if two phenotypically normal heart dogs are bred, and the same results occur as to SAS, what do you do? I believe that it should be our aim to decrease the occurrence of SAS by eliminating dogs with heart murmurs ( SAS ) from the breeding program. I worry that in some cases the decision may be premature, i.e. before 5 months of age, such that puppies which may have a great deal to add to the breed are placed in a non-breeding environment. If in doubt it would be prudent to seek the best veterinary advice available to the owner/breeder i.e. seek the advice of a specialist in cardiology who has all the sophisticated equipment to accurately diagnose the problem. Dr. P.K. St. John DVM  

Also check out this link to another article about SAS by the ARC. HERE

And another HERE