Turning to results, third quarter total Company sales of $1.3 billion increased 14% on a constant-currency basis versus the year-ago period.
In TAVR, third quarter global sales were $508 and $58 million dollars, up 14% on an underlying basis versus the year-ago period.
Globally, our average selling price remained stable.
In the U.S., our TAVR sales grew 12% on a year-over-year basis and we estimate that our share of procedures was stable.
Our TAVR sales in July benefited from encouraging signs of continued recovery from the pandemic, however procedures were negatively impacted in the last two months of Q3 due to the significant impact Delta had on hospital resources.
Outside the U.S. in the third quarter, our sales grew approximately 20% on a year-over-year basis, and we estimate total TAVR procedure growth was comparable.
It's worth noting that recently, published guidelines from the European Association of Cardiothoracic Surgery not definitively recommend TAVR for patients over the age of 75.
The acknowledgment by the Surgical society the TAVR is preferred for those over 75 is a significant development.
We continue to expect underlying TAVR sales growth of around 20% in 2021.
The long-term potential reinforces our view that this global TAVR opportunity will exceed $7 billion by 2024, which implies a low double-digit compound annual growth rate.
Now, turning to TMTT, we've made meaningful progress across all our platforms with over 6000 patients treated to date, to transform treatment and unlock the significant long-term growth opportunity.
In addition, 30-day outcomes for mitral repair with PASCAL from our Miclast, post-market clinical follow-ups study of over 250 patients.
Turning to the financial performance in TMTT, despite the impact of Delta in summer seasonality, global sales of $22 million were driven by the continued adoption of PASCAL in Europe.
We continue to expect to achieve our previous full-year guidance of $80 million to $100 million and estimate the global TMTT opportunity to triple to approximately $3 billion by 2025.
In Surgical Structural Heart, third quarter global sales were $217 million, up 6% on an underlying basis versus the year-ago period.
Registry data confirmed excellent real-world outcomes with INSPIRIS RESILIA in patients under the age of 60.
In Critical Care, third quarter global sales were $213 million up 17% on an underlying basis versus the year-ago period.
Total sales in the third quarter grew 14% on an underlying basis over the prior year.
Earnings in the quarter of $0.54 met our expectations as COVID -related constrained spending more than offset lower-than-expected sales.
And our October procedure trends, we're projecting total Q4 sales of between 1.30 billion and 1.38 billion.
A as it relates to each product line, we are forecasting fourth quarter TAVR sales of $850 million to $910 million and still have the potential to reach underlying TAVR sales growth of around 20% for the full-year 2021.
We continue to expect our full-year adjusted earnings per share guidance at the high-end of $2.07 to $2.27 with fourth-quarter adjusted earnings per share of 53 to 59 cents.
Our adjusted gross profit margin was 76.3% up from 75.5% in the same period last year when we experienced substantial costs responding to COVID, the improvement was also driven by a more profitable product mix, partially offset by a negative impact from foreign exchange.
We continue to expect our 2021 adjusted gross profit margin to be between 76% and 77%.
Selling general and administrative expenses in the third quarter were $364 million or 27.8% of sales compared to $307 million in the prior year.
We still expect full-year 2021 SGNA expenses as a percentage of sales excluding special items to be 28% to 29%.
Research and development expenses in the quarter grew 22% over the prior year to $238 million or 18.2% of sales.
For the full-year 2021, we continue to expect R&D expenses as a percentage of sales to be 17% to 18%.
Our reported tax rate this quarter was 13% or 13.9%, excluding the impact of special items.
We continue to expect our full-year rate in 2021, excluding special items to be between 11% and 15%, including an estimated benefit of four percentage points from stock-based compensation accounting.
Foreign exchange rates increased third quarter reported sales growth by 70 basis points for $8 million compared to the prior year.
At current rates, we continue to expect an approximate $70 million positive impact, or about 1.5%, to full-year 2021 sales, compared to 2020.
Foreign exchange rates negatively impacted our third quarter gross profit margin by 30 basis points compared to the prior year.
Free cash flow for the third quarter was $471 million, defined as cash flow from operating activities of $532 million less capital spending of $61 million our year-to-date free cash flow was $1.1 billion.
We continue to maintain a strong and flexible Balance Sheet with approximately $3 billion in cash and investments as of September 30th.
Average shares outstanding during the third quarter were 632 million and we continue to expect our average diluted shares outstanding for 2021 to be at the lower end of our 630 to 635 million guidance range.
We have approximately $1.2 billion remaining under the share repurchase program.

Summary:
Turning to results, third quarter total Company sales of $1.3 billion increased 14% on a constant-currency basis versus the year-ago period.
Globally, our average selling price remained stable.
Our TAVR sales in July benefited from encouraging signs of continued recovery from the pandemic, however procedures were negatively impacted in the last two months of Q3 due to the significant impact Delta had on hospital resources.
Earnings in the quarter of $0.54 met our expectations as COVID -related constrained spending more than offset lower-than-expected sales.
We continue to expect our full-year rate in 2021, excluding special items to be between 11% and 15%, including an estimated benefit of four percentage points from stock-based compensation accounting.