Diclofenac Associated With Increased Risk for Cardiovascular Events

Among NSAIDs, those with dominant COX-1 activity ( Ibuprofen and naproxen) but not those with dominant Cox-2 activity (diclofenac , voltaren) interfere with the cardioprotective effects of aspirin . 

The nonsteroidal anti-inflammatory drug (NSAID) diclofenac, a drug that is frequently used for the treatment of pain and inflammation caused by arthritis, is associated with a significantly increased risk of cardiovascular complications.
Diclofenac increased the risk of cardiovascular events between 38% and 63% in different studies. The increased risk with diclofenac was similar to the COX-2 inhibitor rofecoxib (Vioxx, Merck), a drug withdrawn from worldwide markets because of cardiovascular toxicity.
In patients with prior myocardial infarction (MI), most nonsteroidal anti-inflammatory drugs (NSAIDs), even when taken for as little as 1 week, are associated with an increased risk for death and recurrent MI.
So NSAIDs are still dangerous to patients with a history of MI, even five years after their event. I would say there is no safe treatment window for these patients, and even short-term treatment with an NSAID is hazardous.

references 
1-McGettigan P, Henry D. Use of non-steroidal anti-inflammatory drugs that elevate cardiovascular risk: An examination of sales and essential medicine lists in low-, middle-, and high-income countries. PLoS Med 2013; DOI:10.1371/journal.pmed.1001388.

2-Schjerning Olsen A, Fosbøl L, Lindhardsen J, et al. Long-term cardiovascular risk of NSAID use according to time passed after first-time myocardial infarction. A nationwide cohort study. Circulation 2012; DOI: 10.1161/​CIRCULATIONAHA.112.112607.