The only thing I can really think of that you might be describing is the result of the Valsalva maneuver. During exercise, if you hold your breath (by closing your epiglottis), it can cause a rather extreme spike in blood pressure. While proper breathing techniques alleviate this, it is especially important for those that suffer from cardiovascular disease (CVD) because a spike in blood pressure on the level of that caused by the valsalva can lead to cardiac arrest.
There is also the possibility that underlying CVD, primarily high blood pressure, can cause the heart to have to work so hard during both resistance and cardio training to overcome blood pressure problems that the heart itself actually increases in size*, which is another sign/symptom of CVD and extremely unhealthy as the heart now requires more oxygen to function and can lead to further complications.
*Not to be confused with the increase in atrium/ventricle volume that occurs in response to aerobic fitness training.