Based on the data found in the USA from the Great Dane National heart scanning clinic conducted over 4 years. Approximately 63% were classed as normal when scanned. Results have been published so far for 2008, 2009 & 2010. As this clinic is conducted at a show this means that a large % of the Danes scanned were of breeding age. The owners were not aware of any issues and would potentially breed from these animals. That means that potentially 37% classed as abnormal could have found their way in to the breeding gene pool.
The theory of only breeding from animal with good hip scores and therefore over time improveing the hip status of the breed can also be applied here. If we only breed from animal that pass an annul heart scan we could improve that heart status of our breed. The data also shows that there were a number of Danes that were diagnosed with DCM in these sessions. The current research is suggesting the DCM is an autosomal dominate gene, as with Doberman DCM. That means that you only need one copy of the gene to have the condition and therefore its recommended that any Dane with the condition should not be bred from.
You will be able to read more about DCM here but we are aware that it is usually a late onset disease meaning you may have bred from your Dane before your aware of the problem. You can also read here about an account of DCM in a younger Dane and the American data also suggest that there are exceptions to the rule.
If by scanning we are able to remove these odd cases from the breeding gene pool it will be a step in the right direction.