It generally wouldn't but if you were already atherosclerotic, thicker blood would clot more easily and cause a myocardial ischemia
or infarct. If you have a healthy heart and blood vessels thicker blood would take a long time to have a direct effect on your heart. And then it would only increase the work load on the ventricles and cause them to hypertrophy. But I can't see a situation where your blood would be so thick for so long.
By "thicker" blood I'm assuming you mean an increased red cell and hemoglobin
content. Your hematocrit
would have to be 55% or higher for it to be called "thick".